Mention CHANGES.md in PR template explicitly (#3295)
Mention CHANGES.md in PR template explicitly (#3295)

This makes the location more explicit which hopefully makes the PR
process smoother for other first time contributors.

Co-authored-by: Jelle Zijlstra <0abdc8e23dddf9bc5a9580b02578de47fa5ab096@gmail.com>
psf/black