Create gentropy doc pages for the quality control flags

[DSuveges]

There is a growing number of quality flags indicating concerns about studies and study-loci. The interpretation of these quality flags not always trivial, and in general there should be a documentation on them. The scope of this ticket is to create new doc. page for gentropy (https://opentargets.github.io/gentropy) to list and explain these flags.

Tasks:

• [ ] Review current set of quality control flags.
• [ ] Amend description and docstring wherever it needed.
• [ ] Create new pages in the documentation

[DSuveges]

Na, this is not an issue, the documentation is already there: