Option to watch folders

[senntore]

Is your feature request related to a problem? Please describe.
I like viewing my books from Foliate's library view but right now we have to either add books to Foliate or use another file system to open them in Foliate.

Describe the solution you'd like
It would be great if you can implement an option to watch certain folders like Documents, etc.
This would enable Foliate to automatically add/remove books from it's library view depending on the changes made in selected folders.