Remove or update conda-forge package

[jan-david-fischbach]

Provide a minimally reproducible example

Run the introduction walkthrough but install nbdev from conda-forge.
Github Actions will fail. See for example https://github.com/Jan-David-Black/javiche/actions/runs/4063947811/jobs/6996780781

[jan-david-fischbach]

In the repo I reinstalled nbdev from the fastai channel and started over, which makes it work. However an install from conda-forge should be avoided

[seeM]

The conda-forge package seems to be maintained by a third party: https://github.com/conda-forge/nbdev-feedstock, so I'm not sure what we could do about that.

The tutorial does suggest to install from the fastai channel: conda install -c fastai nbdev. Perhaps we could include a note/warning in the docs?