branch: deprecate --set-upstream and show help if we detect possible mistaken use

diff --git a/RelNotes b/RelNotes
index 3d420845b117b3f3eb82d1f0948a61c7989d8af9..19bb2ebbe687d9ded1a5c82d28d4410de1e2f19f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.6.1.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.12.txt
\ No newline at end of file