Add triagebot configuration
Add triagebot configuration

This enables assignment through triagebot on this repository, in preparation for
the migration from highfive to triagebot for PR assignment.

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