[7.14] Add release notes for 7.13.4

Co-authored-by: Seth Michael Larson <seth.larson@elastic.co>

Author: github-actions[bot]

docs/guide/release-notes.asciidoc

@@ -1,6 +1,7 @@
 [[release-notes]]
 == Release notes
 
+* <<rn-7-13-4>>
 * <<rn-7-13-3>>
 * <<rn-7-13-2>>
 * <<rn-7-13-1>>
@@ -27,6 +28,12 @@
 * <<rn-7-0-0>>
 
 
+[discrete]
+[[rn-7-13-4]]
+=== 7.13.4 (2021-07-20)
+
+* Client is compatible with Elasticsearch 7.13.4
+
 [discrete]
 [[rn-7-13-3]]
 === 7.13.3 (2021-07-07)