custom-named-profiles: add documentation in unstable.md
custom-named-profiles: add documentation in unstable.md

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