git branch --edit-description a custom file

Hi all,

It seems like everyone working on git.git has their own patch management system. Currently, I keep all of my branch-specific configurations (including CC lists) and patches in a worktree within the repo so that I can keep my configs synced around on different computers.

One thing that's missing about this setup is that I would like to version my branch descriptions as well since I use those to generate cover letters. Unfortunately, `git branch --edit-description` only operates on .git/config.

As a workaround, I rewrote `git branch --edit-description` as a shell-script that can operate on any config file but I feel like a more general solution should be warranted.

Would changing the option to `git branch --edit-description[=<config>]` make sense, where the `<config>` is optional but if it's specified, it'll operate on that file instead of the .git/config.

Alternately, would it make sense to support a $GIT_CONFIG environment variable globally? That is, when $GIT_CONFIG is specified, git will read/write from $GIT_CONFIG instead of .git/config? It'd be a little heavy-handed for me to make the change just for this one use-case but perhaps people may find other uses for it?

Thoughts?

-Denton