changes.src: document POPCNT fix.

Add POPCNT fix to release notes.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/doc/changes.src b/doc/changes.src
index f718a94..0a44844 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -21,6 +21,8 @@
 
 \b Fix crash on \c{%ifmacro} without an argument.
 
+\b Correct the arguments to the \c{POPCNT} instruction.
+
 
 \S{cl-2.05.01} Version 2.05.01