Document how to add notes / reasons for individual annotations

[kasnerz]

Currently, the model can produce the reason or note field for each annotation.

This note is then visible on mouse hover in the Browse interface.

However, this feature is currently undocumented.

[kasnerz]

Instructions are now on wiki - https://github.com/ufal/factgenie/wiki/03-LLM-Annotations#-configuring-the-prompt