[debops] Installation instructions need to be updated

[Alphix]

The setup.py file comments:

debops/setup.py

Line 10 in 5abfaaf

# pip3 install --user --editable .

indicate that for development, you should run pip3 install --user --editable .

Similar instructions are provided here.

Since bookworm, PEP668 has been implemented, meaning that the above instructions will just give this result:

    error: externally-managed-environment
  
    × This environment is externally managed
    ╰─> To install Python packages system-wide, try apt install
        python3-xyz, where xyz is the package you are trying to
        install.
  
        If you wish to install a non-Debian-packaged Python package,
        create a virtual environment using python3 -m venv path/to/venv.
        Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
        sure you have python3-full installed.
  
        If you wish to install a non-Debian packaged Python application,
        it may be easiest to use pipx install xyz, which will manage a
        virtual environment for you. Make sure you have pipx installed.
  
        See /usr/share/doc/python3.11/README.venv for more information.
  
    note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
    hint: See PEP 668 for the detailed specification.

I know I can use a venv (or pipx, or --break-system-packages), but the instructions should be updated. Not sure which approach you prefer @drybjed?