Auto merge of #5219 - mbrubeck:doc, r=alexcrichton
authorbors <bors@rust-lang.org>
Wed, 21 Mar 2018 18:48:39 +0000 (18:48 +0000)
committerbors <bors@rust-lang.org>
Wed, 21 Mar 2018 18:48:39 +0000 (18:48 +0000)
Fix usage text for cargo install

The current text was accidentally copied from `cargo init`.


Trivial merge