[Doc] migration guide joda

docs/reference/migration/migrate_7_0/java_time.asciidoc

@@ -89,6 +89,7 @@ When you are running Elasticsearch 7 with Java 8, you are not able to parse
 the timezone `GMT0` properly anymore. The reason for this is a bug in the
 JDK, which has not been fixed for JDK8. You can read more in the
 https://bugs.openjdk.java.net/browse/JDK-8138664[official issue]
+This bug is fixed in JDK9 and later versions.
 
 [float]
 ==== Scripting with dates should use java time based methods
@@ -125,3 +126,10 @@ and should be replaced.
 
 With the switch to java time, support for negative timestamps has been removed.
 For dates before 1970, use a date format containing a year.
+
+
+[float]
+==== Migration guide
+For a detailed migration guide, see <<migrate-to-java-time>>.
+
+include::migrate_to_java_time.asciidoc[]