Auto merge of #4523 - dbrgn:badges-docs, r=matklad
authorbors <bors@rust-lang.org>
Sun, 24 Sep 2017 20:10:35 +0000 (20:10 +0000)
committerbors <bors@rust-lang.org>
Sun, 24 Sep 2017 20:10:35 +0000 (20:10 +0000)
Improve docs for build badges

The `repo` format wasn't clear to me. I also fixed a typo and clarified how the is-it-maintained badges are generated


Trivial merge