Update the Release Notes with Java 7 requirement

Change-Id: Id38bf628d403afe7a718bb7a686dffc7de2481a9

ReleaseNotes/ReleaseNotes-2.9.txt

diff --git a/ReleaseNotes/ReleaseNotes-2.9.txt b/ReleaseNotes/ReleaseNotes-2.9.txt
index e4aa124..83da601 100644
--- a/ReleaseNotes/ReleaseNotes-2.9.txt
+++ b/ReleaseNotes/ReleaseNotes-2.9.txt
@@ -8,6 +8,10 @@
 https://gerrit-releases.storage.googleapis.com/gerrit-2.9.war]
 
 
+*WARNING:* Support for Java 1.6 has been discontinued.
+As of Gerrit 2.9, Java 1.7 is required.
+
+
 Schema Change
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