Added some cross-references to the end.

Doc/lib/libshelve.tex

@@ -62,3 +62,9 @@ be used to solve this, but this differs across \UNIX{} versions and
 requires knowledge about the database implementation used.
 
 \end{itemize}
+
+
+\begin{seealso}
+  \seemodule{pickle}{Object serialization used by \module{shelve}.}
+  \seemodule{cPickle}{High-performance version of \module{pickle}.}
+\end{seealso}