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`.
+
+Next, either install stylelint-config-eyeo within your project. For example:
+
+    npm install --save-dev stylelint-config-eyeo

[Thomas Greiner, 2017/09/15 16:58:29]

Is this worth mentioning? Considering that there are many different ways on how
you can use the package, we may end up documenting installation instructions for
all possible scenarios (e.g. --save, --save-optional, grunt, gulp).

Therefore I'd assume that mentioning a single use-case (in this case as a global
module) and leaving the rest up to the user might be sufficient but I don't know
for sure. What do you think?

[ire, 2017/09/18 07:36:20]

I was trying to follow the style that was used in stylelint's
stylelint-config-standard and stylelint-config-recommended . They mention both
options (although not for the `npm install` part, just the usage part). 

Also, the reason I thought it better to include both, is because of the
difference between how stylelint configs are extended and how eslint configs are
extended. It can be a bit confusing because it seems like stylelint configs
installed globally need to have an absolute path, whereas eslint configs do not.
And if we mention installing only locally/globally, people may get a bit mixed
up. 

[Thomas Greiner, 2017/11/14 13:18:31]

Sounds reasonable.

+
+Or, install stylelint-config-eyeo globally. For example:
+
+    npm install --g stylelint-config-eyeo

[Thomas Greiner, 2017/09/15 16:58:29]

Detail: This should be either `-g` or `--global`.

[ire, 2017/09/18 07:36:20]

Good catch, I meant `-g`. Done.

+
+## 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`.