Python API instructions

;;;
;;; To use the Python API in sortsmill-editor, put
;;;
;;;     (use-modules (sortsmill python)
;;;                  (sortsmill usermenu python))
;;;     (use-python-api)
;;;     (load-user_init.py)
;;;     (load-python-scripts-directory)
;;;
;;; in your user-init.scm.
;;;