QoL/Bug : stack-pr only searches for config in the same directory it is in

[cheshire]

Probably it should look in the root .git directory, since that's where all config files are stored. This results in non-obvious errors when stack-pr is invoked from any non-root directory.

[smudge]

It might even make sense to search up the file tree until ~. This would allow for global configs, assuming that it would not be unexpected for configs to get merged (in priority order of nearest to furthest from pwd).