Add a note to JupyterHub spawn links using nbpuller to use HTML encoded URLs

The page for pulling git repositories using the JupyterHub Spawn Link, together with nbpuller, uses raw-formatted URLs.

The default for nbpuller is to encode URLs to valid HTML, using HTML encoding (see the nbgitpuller link generator).

This should be added to the compendium.

E.g., raw link:

https://taurus.hrsk.tu-dresden.de/jupyter/hub/user-redirect/git-pull?repo=https://github.com/jdwittenauer/ipython-notebooks&urlpath=/tree/ipython-notebooks/notebooks/language/Intro.ipynb#/~(partition~'interactive~environment~'test)

and HTML encoded Link:

https://taurus.hrsk.tu-dresden.de/jupyter/hub/hub/user-redirect/git-pull?repo=https%3A%2F%2Fgithub.com%2Fjdwittenauer%2Fipython-notebooks&urlpath=tree%2Fipython-notebooks%2F%2Ftree%2Fipython-notebooks%2Fnotebooks%2Flanguage%2FIntro.ipynb#/~(partition~'interactive~environment~'test)

I have seen a kinds of strange errors (see e.g. #9895) when the raw URL is added to HTML-pages, or send via HTML-Mails to students/participants.