Added a synopsis.
diff --git a/Doc/lib/libzlib.tex b/Doc/lib/libzlib.tex
index 718a3d4..0369507 100644
--- a/Doc/lib/libzlib.tex
+++ b/Doc/lib/libzlib.tex
@@ -1,10 +1,11 @@
% XXX The module has been extended (by Jeremy) but this documentation
-% hasn't been updated yet
+% hasn't been updated completely.
\section{Built-in Module \module{zlib}}
\declaremodule{builtin}{zlib}
-\modulesynopsis{None}
+\modulesynopsis{Low-level interface to compression and decompression
+routines compatible with \program{gzip}.}
For applications that require data compression, the functions in this