Auto merge of #2852 - alexcrichton:doc-env-vars, r=alexcrichton
authorbors <bors@rust-lang.org>
Mon, 11 Jul 2016 16:57:49 +0000 (09:57 -0700)
committerGitHub <noreply@github.com>
Mon, 11 Jul 2016 16:57:49 +0000 (09:57 -0700)
Document the RUSTC/RUSTDOC build script env vars


Trivial merge