change hardcoded master branch in readme enumeration to HEAD

diff --git a/RelNotes b/RelNotes
index 80ae7a3110de6bd298cfa9d8481808d0af5e7d2d..fc657e7d2f4b22ce71b2983bd33d9fca131c0c37 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.15.0.txt
\ No newline at end of file
+Documentation/RelNotes/2.24.0.txt
\ No newline at end of file