Add a warning against compression in config.h
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index c22830b..8b6a862 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -345,6 +345,10 @@
* If set, the SSL/TLS module uses ZLIB to support compression and
* decompression of packet data.
*
+ * \warning TLS-level compression MAY REDUCE SECURITY! See for example the
+ * CRIME attack. Before enabling this option, you should examine with care if
+ * CRIME or similar exploits may be a applicable to your use case.
+ *
* Used in: library/ssl_tls.c
* library/ssl_cli.c
* library/ssl_srv.c