Adding docs about cleanup_saved_downloads

Author: bsipocz

docs/testing.rst

@@ -101,3 +101,13 @@ This file only needs the ``get_package_data()`` function, which will tell
         paths_test = [os.path.join('data', '*.xml')]
 
         return {'astroquery.module.tests': paths_test}
+
+
+Doctesting
+----------
+
+Narrative documentation should also be tested, the ``doctest-remote-data`` directive provides a way
+to mark code snippets that relies on remote data access.
+
+If any of the examples include saving data files locally, use the ``testcleanup`` directive and the
+`~astroquery.utils.cleanup_downloads.cleanup_saved_downloads` function at the end of the narrative documentation.