Improve comment about isgci database location

Author: tobiasdiez

src/sage/graphs/isgci.py

@@ -852,12 +852,8 @@ def update_db(self):
 
         This method downloads the ISGCI database from the website
         `GraphClasses.org <http://www.graphclasses.org/>`_. It then extracts the
-        zip file and parses its XML content.
-
-        Depending on the credentials of the user running Sage when this command
-        is run, one attempt is made at saving the result in Sage's directory so
-        that all users can benefit from it. If the credentials are not
-        sufficient, the XML file are saved instead in the user's directory.
+        zip file and parses its XML content. The XML file is saved in the directory
+        controlled by the :class:`DatabaseGraphs` class (usually, ``$HOME/.sage/db``).
 
         EXAMPLES::