Update "how to file bugs"

Summary:
We want users to use Ponder as primary support vector.

T15084

Test Plan: Generated diviner, saw that the reference works correctly.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25125