changes.src: document %00 fix

Add %00 fix to release note.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
diff --git a/doc/changes.src b/doc/changes.src
index 47fb03b..3dc85de 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -25,6 +25,8 @@
 where one or more parts result from empty token expansion, resulting
 in \c{%+} tokens at the beginning or end, or multiple ones in a row.
 
+\b Fix macro label capture (\c{%00}, \k{percent00}).
+
 \b Portability fixes.
 
 \S{cl-2.15.02} Version 2.15.02