Support sioyek extensions

[kchousos]

The sioyek flatpak doesn't recognize the python packages installed with pip on the host. So, the extensions cannot be run. Is there any fix for this?

[nbenitez]

Are these the extensions you want to use?
https://github.com/ahrm/sioyek-python-extensions

I think we can add them to the Sioyek flatpak package then..