Add links to parent/child and nested

Author: honzakral

examples/README.rst

@@ -19,7 +19,10 @@ For simplicity we use a timestamp as version in the index name.
 -------------------
 
 More complex example highlighting the possible relationships available in
-elasticsearch - parent/child and nested.
+elasticsearch - `parent/child
+<https://www.elastic.co/guide/en/elasticsearch/reference/6.3/nested.html>`_ and
+`nested
+<https://www.elastic.co/guide/en/elasticsearch/reference/6.3/nested.html>`_.
 
 ``composite_agg.py``
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