doc add explanation missing from per context provate data

Signed-off-by: Andy Green <andy.green@linaro.org>

diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index 77afd84..8b98d90 100644 (file)
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -546,6 +546,9 @@ struct libwebsocket_protocols {
  * @per_session_data_size:     Libwebsockets will auto-malloc this much
  *                             memory for the use of the extension, a pointer
  *                             to it comes in the @user callback parameter
+ * @per_context_private_data:   Optional storage for this externsion that
+ *                             is per-context, so it can track stuff across
+ *                             all sessions, etc, if it wants
  */
 
 struct libwebsocket_extension {