Pull Request Tips
I think these issues pop up on a good deal of PRs but aren't explicitly stated anywhere, so adding a few bullet points to the contributing guide might help
LGTM yep good idea. maybe also something about raising an issue for discussion before submitting a pull request if there is not already an issue on the subject. Follow-up: I would link to this document in the PR template. thanks @WillAyd 

if you can followup with @gfyoung suggestion would be great.