Auto merge of #5051 - cardoe:fix-doc-instructions, r=matklad
authorbors <bors@rust-lang.org>
Mon, 19 Feb 2018 21:39:17 +0000 (21:39 +0000)
committerbors <bors@rust-lang.org>
Mon, 19 Feb 2018 21:39:17 +0000 (21:39 +0000)
update contributing to show how to build the docs

The contributing guide referenced a script that was deleted in
1271bb4de0c0 so it wasn't possible to follow the contributing guide
successfully prior to contributing doc improvements.


Trivial merge