[DOC] add documentation on how to enable multiple language parsing

[ngsikai]

Adding documentation for #122

Question

The syntax option for stylelint includes: "sass"|"scss"|"less"|"sugarss"|"html"|"styled"|"jsx". Is there a need to add the last three options as supported extensions when syntax is not passed in?

[billybonks]

lets add tests for the last 3

[ngsikai]

UPDATE: Added support and test examples for html and styled-components.

In order to support styled-components, I had to bump up the stylelint version in package.json.

Attempted adding support to jsx but had some errors popping up from postcss. I have the WIP stashed on a local branch in case we want to revisit it again in the future.

[billybonks]

lets just rebase.