automate initialization of git repo

[egpbos]

Checklist before submitting an issue

• [x] I have checked the existing issues and couldn't find an issue about this bug.

Issue details

The current template after generation gives a nice set of follow-up instructions on how to initialize a git repository and sync to GitHub. I think it would be cool if we automate that as well. Could be optional. This also supports better the updating functionality, which is dependent on having a git repository. If you try it without git repo, copier says:

[egpbos]

Apologies, this is a duplicate of #537.