Added sample script to create or activate virtual environment.

    deactivate

Eventually create the following script that activates the envioronment,

or creates it if not present yet:

    #

    # Source this script to setup:

    #

    #    .  this_script

    #

    # virtual environment exists already?

    if [ -f .venv/bin/activate ]; then

      # activate:

      source .venv/bin/activate

    else

      # eventually enable latest python version:

      #module load python/3.13.1

      # init virtual environment:

      python3 -m venv --prompt cso .venv

      # activate:

      source .venv/bin/activate

      # upgrade pip:

      pip install --upgrade pip

      # install local codes:

      pip install --editable .

    fi