Add missing 2.5 release notes section

Change-Id: I129d5414bd7c6db93ea7c2cb795436c55a6d9733

ReleaseNotes/index.txt

diff --git a/ReleaseNotes/index.txt b/ReleaseNotes/index.txt
index 2e4865f..452057c 100644
--- a/ReleaseNotes/index.txt
+++ b/ReleaseNotes/index.txt
@@ -1,6 +1,11 @@
 Gerrit Code Review - Release Notes
 ==================================
 
+[[2_5]]
+Version 2.5.x
+-------------
+* link:ReleaseNotes-2.5.html[2.5]
+
 [[2_4]]
 Version 2.4.x
 -------------