Add known issue to 2.11.4 NEWS file

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>

NEWS

@@ -25,6 +25,14 @@ Inherited from the 2.9 branch:
 
 - Make ganeti-cleaner switch to save working directory (Issue 880)
 
+Known issues
+~~~~~~~~~~~~
+
+The following issue is present in this release and will be fixed before
+the next release.
+
+- Issue 889: Unhandled Xen state '-------'
+
 
 Version 2.11.3
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