Add missing dependency to setup.py, document installation instructions for Fedora

[Kami]

This pull request includes two changes:

1. Add missing dependency to setup.py and requirements.txt

This pull request adds missing pygobject dependency to the setup.py file. This dependency is needed to run the application.

Right now the instructions rely on system level python3-gi package being installed which means it won't work in virtual environments without installing pygobject PyPi package or relying on system site packages (which is not ideal and not the default behavior anymore).

Keep in mind that this will still work even if --system-site-packages and OS level approach is used since that package will already be available in virtual environment.

2. Add installation instructions for Fedora

It adds installation instructions which documents which system level package dependencies are needed on Fedora.