python: Add no-install usage instructions

It's not encouraged, but it's legitimate to want to know how to do.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-id: 20210629214323.1329806-7-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>