Add docstrings

[hello-amal]

Multiple files (e.g., see this comment) have inconsistent or nonexistant docstrings. We should add detailed docstrings to all files, to lower the learning curve for new users of this code.

In the past, I've used pylint to enforce the existence of docstrings, although it doesn't analyze the contents of the docstring. In my experience, pylint wasn't easy to incorporate into pre-commit hooks, but could be incorporated into Github Actions using e.g.,

      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          pip install pylint
          pip install overrides
      - name: Analysing the code with pylint
        run: |
          pylint --recursive=y --rcfile=.pylintrc . --disable fixme --disable import-error