Update README.md (using the Drupal template) and module page for 10.x

Problem/Motivation

Module page and README are outdated I think and do not reflect the current state of the module (10.x-dev - maybe we should create 11.x?).

While it makes sense to use parts of the information on the module page as inspiration for future functionality, the module page and README should reflect the actual functionality.

So after digging into the module, we should update both to be at least basically useful. Features that will work soon can be marked *soon* already.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes