Comments proposal (#198)

Proposal as accepted by core team on 2021-02-19.

Author: zygoloid

proposals/README.md

@@ -57,6 +57,7 @@ request:
     -   [0175 - Decision](p0175_decision.md)
 -   [0179 - Create a toolchain team.](p0179.md)
     -   [0179 - Decision](p0179_decision.md)
+-   [0198 - Comments](p0198.md)
 -   [0199 - String literals](p0199.md)
 
 <!-- endproposals -->