Auto merge of #670 - tmfink:doc-fix, r=emilio
Auto merge of #670 - tmfink:doc-fix, r=emilio

Clarify wording of command line help

I tried to make the wording more consistent and easier to read.

emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen