Docs/readthedocs: install pymediainfo to make autodoc work

Currently, we get:
WARNING: autodoc: failed to import module 'pymediainfo'; the following exception was raised:
No module named 'pymediainfo'

.readthedocs.yaml

@@ -23,3 +23,5 @@ sphinx:
 python:
   install:
     - requirements: docs/requirements.txt
+    # Install pymediainfo itself to make autodoc work
+    - path: .