Add note explaining what comes with the venv

On doing Assignment #1, it's not clear what libraries should be used. We should be suggesting pandas, since we've already included it in our dependencies file.

Start by reading Assignment #1 and the repository's dependencies file to confirm that pandas is included. Update the relevant course note so learners know what the virtual environment provides and that pandas is suggested; done means the guidance is clear and matches the dependency list.

Written by the indexing model from the issue text.