Add how to list installed collection version
Still a bit unsure if this is the right way to do it, but it at least seems to be working good enough:
$ ansible-galaxy collection list -p ./collections | grep sigsum
sigsum.ansible 1.0.4
# /home/rgdd/src/git.sigsum.org/ansible/collections/ansible_collections
sigsum.ansible 1.1.0
I'm a bit unsure how to silence the global installs.