Add entry for copy_reg module.
diff --git a/Doc/lib/libpython.tex b/Doc/lib/libpython.tex
index c58e320..902a092 100644
--- a/Doc/lib/libpython.tex
+++ b/Doc/lib/libpython.tex
@@ -24,6 +24,9 @@
 \item[pickle]
 --- Convert Python objects to streams of bytes and back.
 
+\item[copy_reg]
+--- Register \code{pickle} support functions.
+
 \item[shelve]
 --- Python object persistency.