Is your feature request related to a problem? Please describe.
I use windows and have set XDG_CONFIG dirs (XDG_CONFIG_HOME, XDG_CACHE_HOME) but gitui isn't honoring them

Describe the solution you'd like
If XDG_CONFIG_HOME is set on any os, use XDG_CONFIG_HOME/gitui as directory for config file. If it is not set, fall back to os default