RelNotes: name the release properly

In the title, we should state for which version this release notes
document is about.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/RelNotes/2.20.0.txt b/Documentation/RelNotes/2.20.0.txt
index 368f5da..28a6863 100644
--- a/Documentation/RelNotes/2.20.0.txt
+++ b/Documentation/RelNotes/2.20.0.txt
@@ -1,5 +1,5 @@
-Git Release Notes
-=================
+Git 2.20 Release Notes
+======================
 
 Backward Compatibility Notes
 ----------------------------