Clarify that bbastov is the style of Hound CI.

Since https://github.com/thoughtbot/guides/tree/master/style and bbastov's style is the same, we should link only to one of them to make things clearer.

`Source Code Layout` corresponds to the thoughtbot formatting section.

Also make it clear that Hound CI uses bbastov's style, which is not clear from their documentation.

Follows discussion at: https://github.com/gitlabhq/gitlabhq/pull/6752