Point top-level RelNotes link at 1.5.1 release notes being prepared.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/RelNotes b/RelNotes
index 4571d0d1cfb5a4170dfc80e9654228acae295129..d5e055de6f26abba256cf32bed8dfb056bc6b29c 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.5.0.txt
\ No newline at end of file
+Documentation/RelNotes-1.5.1.txt
\ No newline at end of file