change hardcoded master branch in readme enumeration to HEAD

diff --git a/RelNotes b/RelNotes
index 7b0f25d4c7422ff9f24daae25f6db598a1259f66..fc657e7d2f4b22ce71b2983bd33d9fca131c0c37 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.16.5.txt
\ No newline at end of file
+Documentation/RelNotes/2.24.0.txt
\ No newline at end of file