Need to update PyQt5 to 5.15.2 for Python 3.9 users

[ffedev]

As Title, I cannot install the requirements on Python 3.9 for PyQt5==5.15.0 as it does not provide the binaries for it.

unless this exact version is required to run the code I suggest either to update requirements.txt or a reminder in the Readme to use a prior version of Python