Merge #408

408: Add triagebot configuration r=Dylan-DPC a=LeSeulArtichaut

This enables [assignment](https://github.com/rust-lang/triagebot/wiki/Assignment) through triagebot on this repository, in preparation for the migration from highfive to triagebot for PR assignment.

cc rust-lang/highfive#258 rust-lang/triagebot#433

Co-authored-by: LeSeulArtichaut <[email protected]>

Author: bors[bot]

triagebot.toml

@@ -0,0 +1 @@
+[assign]