Add utility feature to extract git revision

[chshersh]

This can be helpful to display it with --version option. @int-index implemented this in yt-utils. You can see how it's done here:

• https://github.com/serokell/yt-utilities/pull/113/commits/b14dd70cba6319effe420373ac6bd4ad857459b5

[yorickvP]

Use https://git-scm.com/book/en/v2/Customizing-Git-Git-Attributes#_keyword_expansion