Feature Description
Before checking for a .git directory, use the value of $GIT_DIR

Use Case
This is useful for people who like to use separate version control on files that exist in the same place. We move/rename .git to a separate place, and then export GIT_DIR=/path/to/gitdir, or run git commands with the --git-dir=/path/to/gitdir flag.

Proposed Implementation
None.

Alternatives
I guess a flag would work too, or both.

Ps: gitlogue is cool. Thank you for making it.