A sample .eslintrc file

.eslintrc.js

var OFF = 0, WARN = 1, ERROR = 2;

module.exports = exports = {
    "env": {
        "es6": true
    },

    "ecmaFeatures": {
        // env=es6 doesn't include modules, which we are using
        "modules": true
    },

    "extends": "eslint:recommended",

    "rules": {
        // Possible Errors (overrides from recommended set)
        "no-extra-parens": ERROR,
        "no-unexpected-multiline": ERROR,
        // All JSDoc comments must be valid
        "valid-jsdoc": [ ERROR, {
            "requireReturn": false,
            "requireReturnDescription": false,
            "requireParamDescription": true,
            "prefer": {
                "return": "returns"
            }
        }],

        // Best Practices

        // Allowed a getter without setter, but all setters require getters
        "accessor-pairs": [ ERROR, {
            "getWithoutSet": false,
            "setWithoutGet": true
        }],
        "block-scoped-var": WARN,
        "consistent-return": ERROR,
        "curly": ERROR,
        "default-case": WARN,
        // the dot goes with the property when doing multiline
        "dot-location": [ WARN, "property" ],
        "dot-notation": WARN,
        "eqeqeq": [ ERROR, "smart" ],
        "guard-for-in": WARN,
        "no-alert": ERROR,
        "no-caller": ERROR,
        "no-case-declarations": WARN,
        "no-div-regex": WARN,
        "no-else-return": WARN,
        "no-empty-label": WARN,
        "no-empty-pattern": WARN,
        "no-eq-null": WARN,
        "no-eval": ERROR,
        "no-extend-native": ERROR,
        "no-extra-bind": WARN,
        "no-floating-decimal": WARN,
        "no-implicit-coercion": [ WARN, {
            "boolean": true,
            "number": true,
            "string": true
        }],
        "no-implied-eval": ERROR,
        "no-invalid-this": ERROR,
        "no-iterator": ERROR,
        "no-labels": WARN,
        "no-lone-blocks": WARN,
        "no-loop-func": ERROR,
        "no-magic-numbers": WARN,
        "no-multi-spaces": ERROR,
        "no-multi-str": WARN,
        "no-native-reassign": ERROR,
        "no-new-func": ERROR,
        "no-new-wrappers": ERROR,
        "no-new": ERROR,
        "no-octal-escape": ERROR,
        "no-param-reassign": ERROR,
        "no-process-env": WARN,
        "no-proto": ERROR,
        "no-redeclare": ERROR,
        "no-return-assign": ERROR,
        "no-script-url": ERROR,
        "no-self-compare": ERROR,
        "no-throw-literal": ERROR,
        "no-unused-expressions": ERROR,
        "no-useless-call": ERROR,
        "no-useless-concat": ERROR,
        "no-void": WARN,
        // Produce warnings when something is commented as TODO or FIXME
        "no-warning-comments": [ WARN, {
            "terms": [ "TODO", "FIXME" ],
            "location": "start"
        }],
        "no-with": WARN,
        "radix": WARN,
        "vars-on-top": ERROR,
        // Enforces the style of wrapped functions
        "wrap-iife": [ ERROR, "outside" ],
        "yoda": ERROR,

        // Strict Mode - for ES6, never use strict.
        "strict": [ ERROR, "never" ],

        // Variables
        "init-declarations": [ ERROR, "always" ],
        "no-catch-shadow": WARN,
        "no-delete-var": ERROR,
        "no-label-var": ERROR,
        "no-shadow-restricted-names": ERROR,
        "no-shadow": WARN,
        // We require all vars to be initialized (see init-declarations)
        // If we NEED a var to be initialized to undefined, it needs to be explicit
        "no-undef-init": OFF,
        "no-undef": ERROR,
        "no-undefined": OFF,
        "no-unused-vars": WARN,
        // Disallow hoisting - let & const don't allow hoisting anyhow
        "no-use-before-define": ERROR,

        // Node.js and CommonJS
        "callback-return": [ WARN, [ "callback", "next" ]],
        "global-require": ERROR,
        "handle-callback-err": WARN,
        "no-mixed-requires": WARN,
        "no-new-require": ERROR,
        // Use path.concat instead
        "no-path-concat": ERROR,
        "no-process-exit": ERROR,
        "no-restricted-modules": OFF,
        "no-sync": WARN,

        // ECMAScript 6 support
        "arrow-body-style": [ ERROR, "always" ],
        "arrow-parens": [ ERROR, "always" ],
        "arrow-spacing": [ ERROR, { "before": true, "after": true }],
        "constructor-super": ERROR,
        "generator-star-spacing": [ ERROR, "before" ],
        "no-arrow-condition": ERROR,
        "no-class-assign": ERROR,
        "no-const-assign": ERROR,
        "no-dupe-class-members": ERROR,
        "no-this-before-super": ERROR,
        "no-var": WARN,
        "object-shorthand": [ WARN, "never" ],
        "prefer-arrow-callback": WARN,
        "prefer-spread": WARN,
        "prefer-template": WARN,
        "require-yield": ERROR,

        // Stylistic - everything here is a warning because of style.
        "array-bracket-spacing": [ WARN, "always" ],
        "block-spacing": [ WARN, "always" ],
        "brace-style": [ WARN, "1tbs", { "allowSingleLine": false } ],
        "camelcase": WARN,
        "comma-spacing": [ WARN, { "before": false, "after": true } ],
        "comma-style": [ WARN, "last" ],
        "computed-property-spacing": [ WARN, "never" ],
        "consistent-this": [ WARN, "self" ],
        "eol-last": WARN,
        "func-names": WARN,
        "func-style": [ WARN, "declaration" ],
        "id-length": [ WARN, { "min": 2, "max": 32 } ],
        "indent": [ WARN, 4 ],
        "jsx-quotes": [ WARN, "prefer-double" ],
        "linebreak-style": [ WARN, "unix" ],
        "lines-around-comment": [ WARN, { "beforeBlockComment": true } ],
        "max-depth": [ WARN, 8 ],
        "max-len": [ WARN, 132 ],
        "max-nested-callbacks": [ WARN, 8 ],
        "max-params": [ WARN, 8 ],
        "new-cap": WARN,
        "new-parens": WARN,
        "no-array-constructor": WARN,
        "no-bitwise": OFF,
        "no-continue": OFF,
        "no-inline-comments": OFF,
        "no-lonely-if": WARN,
        "no-mixed-spaces-and-tabs": WARN,
        "no-multiple-empty-lines": WARN,
        "no-negated-condition": OFF,
        "no-nested-ternary": WARN,
        "no-new-object": WARN,
        "no-plusplus": OFF,
        "no-spaced-func": WARN,
        "no-ternary": OFF,
        "no-trailing-spaces": WARN,
        "no-underscore-dangle": WARN,
        "no-unneeded-ternary": WARN,
        "object-curly-spacing": [ WARN, "always" ],
        "one-var": OFF,
        "operator-assignment": [ WARN, "never" ],
        "operator-linebreak": [ WARN, "after" ],
        "padded-blocks": [ WARN, "never" ],
        "quote-props": [ WARN, "consistent-as-needed" ],
        "quotes": [ WARN, "single" ],
        "require-jsdoc": [ WARN, {
            "require": {
                "FunctionDeclaration": true,
                "MethodDefinition": true,
                "ClassDeclaration": false
            }
        }],
        "semi-spacing": [ WARN, { "before": false, "after": true }],
        "semi": [ ERROR, "always" ],
        "sort-vars": OFF,
        "space-after-keywords": [ WARN, "always" ],
        "space-before-blocks": [ WARN, "always" ],
        "space-before-function-paren": [ WARN, "never" ],
        "space-before-keywords": [ WARN, "always" ],
        "space-in-parens": [ WARN, "never" ],
        "space-infix-ops": [ WARN, { "int32Hint": true } ],
        "space-return-throw-case": ERROR,
        "space-unary-ops": ERROR,
        "spaced-comment": [ WARN, "always" ],
        "wrap-regex": WARN
    }
};

OFF, WARN, and ERROR are just variables. I use them as symbolic names for the settings. This is a really old snippet, so you would be better to research the latest version of eslint before using this - it likely does not work.

It throws an error

Are we supposed to add that to our .eslintrc.js file or not?

that is not necessary. it's simply referring to how eslint will interpret them when you run it on the command line.

for example, after you run eslint, you might see something like:
Warning: 1:2 warning More than 2 blank lines not allowed no-multiple-empty-lines
Error: 2:34 error 'pick' is defined but never used no-unused-vars
you can set the error level in your .eslintrc.js (under "rules") like:
"semi": 2

hope that helps.