doc: improve instructions for setting up a dev/test env / remove poetry installer workaround
- Provide more detailed information how to get started with a dev/test env.
- Remove workaround for poetry installer
(pipeline run with cleared cache: https://gitlab.archlinux.org/moson/aurweb/-/jobs/146889)
Signed-off-by: moson-mo mo-son@mailbox.org
Edited by Mario Oenning