Add installation instructions using pip install git+...

[BenjaminRodenberg]

These instructions are especially useful if working in a venv. We had to come up with this approach in precice/tutorials#557 to get pySDC installed & running with a single call of a script.

Using venv is recommended by newer pip versions to not interfere with the system python packages. E.g. for the pip version coming with Ubuntu 24.04.

On Ubuntu 24.04 I get:

$ pip --version
pip 24.0 from /usr/lib/python3/dist-packages/pip (python 3.12)
$ pip install --user pySDC
× 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/python3.12/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.
...

[pancetta]

Appreciated!