Docs: Add a note about rollover issues (#33679)

6.4 has a bad bug where it won't if any of the shards on the node have
been rolled over. This documents that in the known issues for 6.4.0 and
links to the fix in the bug fixes section of 6.4.1.

Relates to #33394

Author: nik9000

docs/reference/release-notes/6.4.asciidoc

@@ -55,8 +55,12 @@ coming[6.4.1]
 //[float]
 //=== Enhancements
 
-//[float]
-//=== Bug Fixes
+[float]
+=== Bug Fixes
+
+Rollover::
+{es} can once again start if any shards on the node have been
+<<indices-rollover-index, rolled over>>. {pull}33394[#33394]
 
 //[float]
 //=== Regressions
@@ -67,8 +71,27 @@ coming[6.4.1]
 [[release-notes-6.4.0]]
 == {es} version 6.4.0
 
+[IMPORTANT]
+.Known issue with Elasticsearch 6.4.0 and rollover
+======================================================
+{es} can't start if any of the shards on the node have been
+<<indices-rollover-index, rolled over>>. (issue: {issue}33316[#33316])
+
+The error message looks like:
+
+[source,txt]
+----
+[2018-08-31T09:00:35,520][ERROR][o.e.b.Bootstrap ] Exception
+org.elasticsearch.ElasticsearchException: java.io.IOException: failed to read [id:##, file:path_to_index/_state/state-##.st]
+...
+Caused by: org.elasticsearch.common.xcontent.XContentParseException: [-1:####] [rollover_info] failed to parse field [some_name]
+----
+
+======================================================
+
 [float]
 === Known issues
+See the important section above.
 
 {es} 6.4.0 fails to start when PEM encoded private key files that have been exported from `PKCS#12`
 keystores are in use. These files can be identified by the existence of lines that start with either