RelNotes: name the release properly

gitster · gitster · commit 0e94dab5be2f · 2018-11-19T08:23:09.000+09:00
In the title, we should state for which version this release notes
document is about.

Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git 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
 ----------------------------
