Update 2.10.3 release notes

Change-Id: I07be2d363b85e0372504b8782fd4be451ed4f486

ReleaseNotes/ReleaseNotes-2.10.3.txt

diff --git a/ReleaseNotes/ReleaseNotes-2.10.3.txt b/ReleaseNotes/ReleaseNotes-2.10.3.txt
index abb8db3..aeaca9d 100644
--- a/ReleaseNotes/ReleaseNotes-2.10.3.txt
+++ b/ReleaseNotes/ReleaseNotes-2.10.3.txt
@@ -108,6 +108,14 @@
 
 * Prevent double authentication for the same public key.
 
+
+Performance
+-----------
+
+* Improved performance when creating a new branch on a repository with a large
+number of changes.
+
+
 Upgrades
 --------