Added documentation for the new functions

doc/wrappers.rst

@@ -849,6 +849,8 @@ Functions
    Permissions on this operation are of course rather strict:
    users can only modify their own password.
    Of course, an administrator can modify the password of every user.
+   Active logins do not need to be refreshed, as the new username will automatically be used everywhere.
+   From the next login, however, the new username has to be used, as the old one has been renamed.
 
    Examples:
 
@@ -950,7 +952,18 @@ Functions
 
 .. function:: user_name(user, username)
 
-   TODO
+   Changes the username of user *user* to *username*.
+   From this point on, the user has been renamed, and all old permissions are inherited.
+   Similar to password management, users can only alter their own username.
+   The administrator can also alter the username of all users.
+   Active logins do not need to be refreshed, as the new username will automatically be used everywhere.
+   From the next login, however, the new username has to be used, as the old one has been renamed.
+
+   Examples:
+
+   * To change the username of user1 to user2.
+
+     >>> user_name("user1", "user2")
 
 Exceptions
 ^^^^^^^^^^