Find and Activate venv

Tries to find and activate a virtual environment either in the current directory or the closest one in the hierarchy.

Example:

• in /foo/bar/baz
• first, checks if /foo/bar/baz/venv/bin/activate is found (and uses that if it is)
• next, tries /foo/bar/venv/bin/activate
• after that, /foo/venv/bin/activate
• if that was not found, outputs an error message

Note: you need to run the script with source (or .), i.e. source activate-env.sh for the environment activation to work.