Added cross-references between the various archive file formats.
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index 5978031..d298f88 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -15,6 +15,9 @@
 programs, such  as those produced by :program:`compress` and :program:`pack`,
 are not supported by this module.
 
+For other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and
+:mod:`tarfile` modules.
+
 The module defines the following items: