branch description as a note?

Hi,

so I've been wondering about branch descriptions being just a local configuration. The only use-case I know for them is generating cover letters and request-pull, although I could imagine maybe the maintainer uses branch descriptions for storing the - well - branch descriptions for the "What's cooking" emails and the merge commit messages.

Now my problem with the description being a local configuration, is that I often work on patches on two different computers. I can easily share my patch notes with myself, but not the branch description. If these could be pushed and fetched like a note, I think that would open up some other nice possibilities as well, like having a standard place for MR/PR messages for forges, sharing proposed merge commit messages, maybe other things.

For my personal issue of sharing branch descriptions with myself, I could probably just make up a convention for myself, say using refs/notes/branches, but it would be nice to have this built in, instead of the local config branch description.

From usage perspective I could imagine a new `--branch` flag for notes, which would tell `git notes` to operate on notes attached to branches instead of specific commits, probably stored under refs/notes/branches by default. Maybe add an `--edit-branch-note` to `git branch`. And of course have the option to use this note instead of the description configuration wherever it makes sense.

What do you think?

Thanks, Bence