Auto merge of #2490 - alexcrichton:rustflags-docs, r=alexcrichton
authorbors <bors@rust-lang.org>
Thu, 17 Mar 2016 01:12:32 +0000 (18:12 -0700)
committerbors <bors@rust-lang.org>
Thu, 17 Mar 2016 01:12:32 +0000 (18:12 -0700)
Add docs for RUSTFLAGS and build.rustflags


Trivial merge