Auto merge of #6403 - ehuss:doc-config-update, r=alexcrichton
Auto merge of #6403 - ehuss:doc-config-update, r=alexcrichton

Minor update to config docs.

rustyhorde/cargo,rust-lang/cargo,eminence/cargo,nipunn1313/cargo,rustyhorde/cargo,tshepang/cargo,vojtechkral/cargo,eminence/cargo,rust-lang/cargo,vojtechkral/cargo,nipunn1313/cargo,eminence/cargo,rustyhorde/cargo,tshepang/cargo,tsurai/cargo,rust-lang/cargo,tsurai/cargo,nipunn1313/cargo,rustyhorde/cargo,tsurai/cargo,rust-lang/cargo,nipunn1313/cargo,tsurai/cargo,tshepang/cargo,tsurai/cargo,vojtechkral/cargo,vojtechkral/cargo,tshepang/cargo,eminence/cargo