Auto merge of #4489 - mattgathu:update_appveyor_badge_docs, r=alexcrichton
authorbors <bors@rust-lang.org>
Wed, 13 Sep 2017 14:02:41 +0000 (14:02 +0000)
committerbors <bors@rust-lang.org>
Wed, 13 Sep 2017 14:02:41 +0000 (14:02 +0000)
Update Appveyor badge docs

* indicate you can specify the appveyor project id if you want to use that instead

This PR is part of: https://github.com/rust-lang/crates.io/issues/693


Trivial merge