conf.py: Try to get improved documentation with automatic API listings.

1 job for master in 6 seconds (queued for 6 seconds)
Name Stage Failure
failed
pages Test
$ cd doc
$ make html
Running Sphinx v4.1.2

Extension error:
Could not import extension nbsphinx (exception: No module named 'nbsphinx')
make: *** [Makefile:20: html] Error 2
Cleaning up file based variables
ERROR: Job failed: exit code 2