Auto merge of #4464 - matklad:document-all-the-things, r=alexcrichton
authorbors <bors@rust-lang.org>
Sat, 9 Sep 2017 19:44:59 +0000 (19:44 +0000)
committerbors <bors@rust-lang.org>
Sat, 9 Sep 2017 19:44:59 +0000 (19:44 +0000)
Mention sccache in the guide

Closes  #4307


Trivial merge