Wrote a more user-friendly Readme file

[annefou]

As a starting point. It can be extended further in the future, especially when we write some documentation for the API and more examples.

[keewis]

pre-commit.ci autofix

[tinaok]

@keewis In the Readme.me, it says pip install xdggs, but it does include the visualisation with it? If not it is may be better to update the pip install that it install the visualisation in default?

[keewis]

Actually, no, it doesn't. I added it as an optional dependency, so we'd need the explore extra. However, if we consider explore to be an integral part of xdggs, we can promote it to a required dependency (in a separate PR, though).

[keewis]

Thinking about it, I think that's the way to go forward – xdggs is not stable enough to care about minimal dependencies right now.

I'll thus merge this now, and follow up with the PR to change the dependencies. Thanks again, @annefou, @tinaok