Add a release note about dropping Java 7 support

Added a release note message indicating that the 6.0.11 release is
the last one that will support Java 7.  Starting with the following
release, we will only support Java  8 or later.

docs/release-notes.html

@@ -13,6 +13,12 @@ <h3>Version 6.0.11</h3>
               </p>
 
               <ul>
+                <li>
+                  Note that this is the last release that will support Java 7.  The next release
+                  (expected to have a version number of 7.0.0) will only support Java 8 and later.
+                  <br><br>
+                </li>
+
                 <li>
                   Updated the Filter methods for creating substring filters to better support empty
                   components.  In LDAP filters, filters are transmitted using a binary encoding,