Add a link to the docs repository

Would be nice if the site could have a link to the relevant markdown file
on GitHub for each page/an issue report link (#400). Seems that
laravel/laravel.com isn't the current website :)
Merge branch 'master' of http://github.com/laravel/docs into docs-contributing
Merge pull request #412 from rmasters/docs-contributing

Add a link to the docs repository