Genereate .copier-answer.yml and add template tag to README

[TimMonko]

Description

This genarates the .copier-answer.yml file which I've been debating on adding for a while. My hesitation is adding yet another file into the template's output, but I'm realizing a few strengths:

1. authors can validate how they set up a project, and use that in a new project, if they find it helpful
2. support, like from the napari team, will be easier because we can see what the project started with, in order to narrow down changes
3. it allows re-running templates and updating, by basing on previous answers or 'resetting'

This also adds the vcs_ref (tag or dev version) to the template output, so that, again, it's easier to support plugin authors.

[DragaDoncila]

I do like this, it seems useful. Agree we have a lot of files generated, but I do think the potential usefulness of this outweighs the cons. Folks can always delete it if they want. It would be nice to do a video tour or blog post or something that takes you through all the different stuff the template sets up. I just ran it today for something and there's so much stuff - can be very intimidating for a beginner