Auto merge of #2669 - mbrubeck:dev-dep-doc, r=alexcrichton
Auto merge of #2669 - mbrubeck:dev-dep-doc, r=alexcrichton

Document that dev-dependencies are used when building examples

None

rustyhorde/cargo,achanda/cargo,rustyhorde/cargo,brson/cargo,AndiDog/cargo,mark-buer/cargo,rust-lang/cargo,sbeckeriv/cargo,brson/cargo,tshepang/cargo,nipunn1313/cargo,tshepang/cargo,sbeckeriv/cargo,sbeckeriv/cargo,sbeckeriv/cargo,tsurai/cargo,nipunn1313/cargo,AndiDog/cargo,tsurai/cargo,AndiDog/cargo,achanda/cargo,eminence/cargo,nipunn1313/cargo,vojtechkral/cargo,durka/cargo,rustyhorde/cargo,achanda/cargo,tsurai/cargo,durka/cargo,vojtechkral/cargo,tsurai/cargo,AndiDog/cargo,mark-buer/cargo,brson/cargo,nipunn1313/cargo,eminence/cargo,tshepang/cargo,vojtechkral/cargo,vojtechkral/cargo,mark-buer/cargo,durka/cargo,tsurai/cargo,eminence/cargo,tshepang/cargo,rustyhorde/cargo,mark-buer/cargo,rust-lang/cargo,eminence/cargo,durka/cargo,AndiDog/cargo,rust-lang/cargo,mark-buer/cargo,rust-lang/cargo,brson/cargo,brson/cargo,achanda/cargo