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

diff --git a/RelNotes b/RelNotes
index e29d6504d9e8fe45d3f7ff7f82f1e8f1f57b9f6f..19bb2ebbe687d9ded1a5c82d28d4410de1e2f19f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.5.6.txt
\ No newline at end of file
+Documentation/RelNotes/1.7.12.txt
\ No newline at end of file