Migrate Wiki from Gitlab to Github

[joergbrech]

There are quite a few links in the README (and the PR template too) referring to the Gitlab Wiki. We should consider migrating (and updating?) the Wiki as well.

In general all README files need cleaning up. There are also a few now dead links to our Gitlab CI artifacts eg in pycode/Readme.rst

[xsaschako]

@mknaranja can this be closed? I think so

[mknaranja]

Yes. Well recognized. Thanks.