Issue 5109 - Create stylelintrc for websites and ui modules

stylelint-config-eyeo/README.md

+# stylelint-config-eyeo
+
+A [Stylelint](https://stylelint.io) configuration that checks for compliance 
+with the [Adblock Plus coding style guide](https://adblockplus.org/coding-style#html-css) 
+which is used for all eyeo projects.
+
+## Installation
+
+    npm install -g stylelint
+
+This command requires administrator privileges so you might need to use `sudo`.

[juliandoucette, 2017/10/13 14:21:06]

NIT: Isn't it a bad idea to give npm administrator privileges?

[ire, 2017/10/24 09:05:16]

The `sudo` is what may be required to run the command. I don't think that's
giving npm administrator privileges (unless I misunderstand how this works?)

Also, I copied this from the eslint-config-eyeo README, so added this for
consistency.

[juliandoucette, 2017/10/26 15:24:08]

sudo is not required to run this command.
Ack. I will file an issue against codingtools.

https://issues.adblockplus.org/ticket/5945

[ire, 2017/10/30 08:30:47]

It depends on the version of npm. In older versions it was more common that
people will need to use `sudo` first (I always had to do this). The comment says
that you "might" need to use it. I don't think it needs to be removed, in case
people are on versions where they do need to use it.

[juliandoucette, 2017/11/01 13:14:26]

On 2017/10/30 08:30:47, ire wrote:

Let's leave this in for now and then remove it as part of
https://issues.adblockplus.org/ticket/5945 if necessary.

[ire, 2017/11/07 07:14:01]

Acknowledged.

+
+Next, either install stylelint-config-eyeo within your project. For example:
+
+    npm install --save-dev stylelint-config-eyeo
+
+Or, install stylelint-config-eyeo globally. For example:
+
+    npm install -g stylelint-config-eyeo
+
+## Usage
+
+To lint a CSS (or CSS-like, e.g. SCSS, SugarCSS, Less) file using Stylelint 
+you run the `stylelint` command with the file as an argument. For example:
+
+    stylelint example.css
+
+For advanced usage see `stylelint --help`.
+
+In order to use stylelint-config-eyeo, your project's Stylelint configuration
+should extend from it. A minimal example looks like this:
+
+    {
+      "extends": "stylelint-config-eyeo"
+    }
+
+If you've globally installed stylelint-config-eyeo using the `-g` flag, then 
+you'll need to use the absolute path to stylelint-config-eyeo in your config.
+
+    {
+      "extends": "/absolute/path/to/stylelint-config-eyeo"
+    }
+
+For projects without a Stylelint configuration you can create your own
+personal configuration in `~/.stylelintrc.json`.