[DOC] fix broken shields in README

[fkiraly]

This PR aims to fix the broken project shields at the top of the readme.

• for now, it is simply a copy from sktime
• this does not include the codecov shields (previously there but not in the fix), but they can be added easily

[fkiraly]

I think this needs to be formatted better, as well - not for merge yet:

• description and logo at the top: I would put them next to each other, so they do not take up space and the links appear quickly
• I moved the quicklinks up, but they are missing a "tutorials" link!
• table and links do not format nicely yet