change hardcoded master branch in readme enumeration to HEAD

diff --git a/RelNotes b/RelNotes
index 6162eb4395ea78354187619db50545c443772b73..fc657e7d2f4b22ce71b2983bd33d9fca131c0c37 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.15.2.txt
\ No newline at end of file
+Documentation/RelNotes/2.24.0.txt
\ No newline at end of file