only triage non-trivial pull requests

the team perceives triaging literally everything as too much overhead,
and there is a desire to allow for more parallel action.

maintainers/README.md

@@ -79,7 +79,8 @@ Items on the board progress through the following states:
 
  If there is disagreement on the general idea behind an issue or pull request, it is moved to _To discuss_, otherwise to _In review_.
 
- To ensure process quality and reliability, all pull requests must be triaged before merging.
+ To ensure process quality and reliability, all non-trivial pull requests must be triaged before merging.
+ What constitutes a trivial pull request is up to maintainers' judgement.
 
 - To discuss