release note update

RELEASES.txt

@@ -242,6 +242,10 @@ Planned
 * Buffer data areas no longer have an automatic NUL terminator to avoid
   rounding user-requested allocation sizes upwards unnecessarily
 
+* Buffer constructor behavior changes: number argument creates a buffer
+  of a certain size; optional second argument indicates whether a buffer
+  should be dynamic or fixed
+
 * Change Array.prototype.splice() behavior so that if 2nd argument
   (deleteCount) is not given, splice to end of array instead of treating
   like deleteCount was zero: the new behavior is non-standard but is the