+1 that Why matters most.

My teammate recently wrote a blog post on how we document Why in git commits and PR descriptions.

https://medium.com/better-programming/daily-habits-to-turn-y...

Would also recommend checking out a related talk by a tech lead at StitchFix: https://confreaks.tv/videos/rubyconf2018-documentation-trade...

"What" is also equally important. But it's covered in the diff itself. Often, there's no need to repeat the diff in text form.