Issue 3692 - Add base ESLint configuration

eslint-config-eyeo/README.md

+# eslint-config-eyeo
+
+An [ESLint](http://eslint.org) configuration that checks for compliance with the
+[Adblock Plus coding style guide](https://adblockplus.org/coding-style#javascript)
+which is used for all eyeo projects.
+
+## Installation
+
+    npm install -g eslint eslint-config-eyeo
+
+(As root, or using sudo.)
+
+## Usage
+
+To lint a JavaScript file using ESLint you simply run the `eslint` command with
+the file as an argument. For example:
+
+    eslint some-file.js
+
+(For advanced usage see `eslint --help`.)
+
+In order to use eslint-config-eyeo your project's ESLint configuration
+should extend from it. A minimal example looks like this:
+
+    {
+      "extends": "eslint-config-eyeo",
+      "root": true

[Sebastian Noack, 2017/02/13 11:31:29]

One could argue, documenting the root option here is out of scope. On the other
hand, pointing it out here might make it easier to get started with ESLint, but
then it seems incomplete, as you have to set the corresponding "env" as well.

[kzar, 2017/02/13 13:02:22]

Well most projects will need more in their configuration but this is a start.
That's why I described it as a minimal example. I guess we could start talking
about env and globals here too but IMO it's out of scope.

+    }
+
+(For projects without an ESLint configuration you can create your own
+personal configuration in `~/.eslintrc.json`, but take care to remove
+the `"root": true` section from the above example.)