Weekly testing of user guide notebooks

[hakonanes]

The new weekly testing of user guide notebooks using nbval works as expected. The action log is here.

The only notebook with cell outputs stored is the "Clustering orientations" one. I would expect all notebooks that haven't stored cell outputs to pass, however some cells in the two other clustering notebooks fail. I'll look into this when I find the time.

[harripj]

Looks like sklearn needs to be installed when using the action: https://github.com/pyxem/orix/runs/6346988629?check_suite_focus=true#step:6:1926

I will add this to the action and run again.

EDIT
I think we need to add the extra "doc" dependencies to the pip install action.

[hakonanes]

Good point. I'll fix this now, as I have to fix setup.py for uploading to PyPI.

[hakonanes]

Fantastic, everything works (log) except the cell in the "Clustering orientations" notebook printing the time for get_distance_matrix(), which we shouldn't expect to be the same for my machine (slightly faster) and the GitHub runner.

[harripj]

We wouldn't expect this to be consistent, but it looks like we can add the tag nbval-ignore-output to the code cell to stop nbval producing the error whilst running the action: https://nbval.readthedocs.io/en/latest/#Using-tags-instead-of-comments

[hakonanes]

Yes, we should add that metadata to the relevant cell!