Update draft release notes to 1.7.7.6

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/RelNotes/1.7.7.6.txt

diff --git a/Documentation/RelNotes/1.7.7.6.txt b/Documentation/RelNotes/1.7.7.6.txt
index 065ed2a..b8b86eb 100644
--- a/Documentation/RelNotes/1.7.7.6.txt
+++ b/Documentation/RelNotes/1.7.7.6.txt
@@ -8,4 +8,9 @@
    directory when two paths in question are in adjacent directories and
    the name of the one directory is a prefix of the other.
 
+ * When producing a "thin pack" (primarily used in bundles and smart
+   HTTP transfers) out of a fully packed repository, we unnecessarily
+   avoided sending recent objects as a delta against objects we know
+   the other side has.
+
 Also contains minor fixes and documentation updates.