Fix MkDocs build

[smokestacklightnin]

Partially addresses #529

This PR solves build failures on Read The Docs by telling git to ignore files that mkdocs/read the docs changes.

This PR does not solve the underlying issue with non-editable installs.

Preview the successfully built docs here

[smokestacklightnin]

Avoiding a dirty index seems to solve the timestamp problem when installing on RTD.

Now I'm getting a very strange error:

WARNING - mkdocs_autorefs: generated/tutorials/gallery_python_api.md: Could not find cross-reference target 'ragna.source_storages.Qdrant'

The line originally read ragna.source_storages.QdrantDB, but fixing it to ragna.source_storages.Qdrant still gives the same error.

Will continue to investigate

Update: I figured it out. "Qdrant" was missing from __all__

[pmeier]

Thanks William, way better fix that what I suggested in #529 (comment). We have a mkdocs hook that shows the files and the respective diff that originates from RTD. However, that relies on git to figure out the changes, which are no longer reported when we --assume-unchanged. Could you add a post_install RTD hook that effectively does git update-index --really-refresh?