Add "what if I have my .gitconfig in version control" to FAQ

[sverch]

First of all, thanks for this project, I've been using it for a while. I have my .gitconfig in version control and I've been using this configuration to not have the key in my .gitconfig:

[ghi]
    token = !bash -c 'echo $GHI_TOKEN'

I thought this might be nice to add to the FAQ. I think I got this from https://stackoverflow.com/a/21574502.