Proposal: (Ab-)using XDG_CONFIG_HOME for roaming .gitconfig settings

[Johannes Schindelin]

Dear Git for Windows users,

a colleague just had a nice idea how support a "roaming .gitconfig": if
we were to default to `%APPDATA%\Git\config` on Windows when the
environment variable `XDG_CONFIG_HOME` is not set, users could edit that
file themselves and take their settings everywhere. I like the idea and
opened a ticket:

https://github.com/git-for-windows/git/issues/316

Please comment there on this idea.

Thanks,
Johannes