`pipx pin` examples is missing from the docs

[stdedos]

Would you mind adding some information about how to use pipx pin?

I don't see many good examples on the docs:

pin gives "4 matching documents", which are:

• pipx pin -h (which doesn't have examples)
• Changelog
• "pipx upgrade-shared examples"
• Home > Credit

and #891 (comment) looks much more pragmatic.

Also if pinning transients is possible (and how)