Added browser extension for GitHub code viewer and editor.

Hi there, I've just published a browser extension that provides EditorConfig support for GitHub:

* [Source code](https://github.com/RReverser/github-editorconfig)
* [Chrome](https://chrome.google.com/webstore/detail/github-editorconfig/bppnolhdpdfmmpeefopdbpmabdpoefjh)
* [Firefox](https://addons.mozilla.org/en-US/firefox/addon/github-editorconfig/)