cloudinit.distros: update docstrings of add_user and create_user

cloudinit/distros/__init__.py

@@ -392,6 +392,9 @@ def get_default_user(self):
     def add_user(self, name, **kwargs):
         """
         Add a user to the system using standard GNU tools
+
+        This should be overriden on distros where useradd is not desirable or
+        not available.
         """
         # XXX need to make add_user idempotent somehow as we
         # still want to add groups or modify SSH keys on pre-existing
@@ -520,9 +523,22 @@ def add_snap_user(self, name, **kwargs):
 
     def create_user(self, name, **kwargs):
         """
-        Creates users for the system using the GNU passwd tools. This
-        will work on an GNU system. This should be overriden on
-        distros where useradd is not desirable or not available.
+        Creates or partially updates the ``name`` user in the system.
+
+        This defers the actual user creation to ``self.add_user`` or
+        ``self.add_snap_user``, and most of the keys in ``kwargs`` will be
+        processed there if and only if the user does not already exist.
+
+        Once the existence of the ``name`` user has been ensured, this method
+        then processes these keys (for both just-created and pre-existing
+        users):
+
+        * ``plain_text_passwd``
+        * ``hashed_passwd``
+        * ``lock_passwd``
+        * ``sudo``
+        * ``ssh_authorized_keys``
+        * ``ssh_redirect_user``
         """
 
         # Add a snap user, if requested