Add external resources doc

Author: swallez

docs/external-resources.md

@@ -0,0 +1,18 @@
+# External resources
+
+<!--
+NOTE TO MAINTAINERS: all versions of the doc point to this file in the main branch.
+There is therefore no need to backport changes, and this file should actually not
+be present in other branches to avoid keeping outdated links around.
+-->
+
+This page aggregates links to material related to the Java API client that provide additional information or different perspectives on the library. [Contributions are welcome](https://github.com/elastic/elasticsearch-java/issues/new?title=New+external+resource).
+
+**Disclaimer**: These links are being provided for informational purposes; they do not constitute an endorsement or an approval by Elastic. Please [let us know](https://github.com/elastic/elasticsearch-java/issues/new?title=Issue+in+external+resources) about links that you think are outdated or inappropriate.
+
+* [ElasticCC platform - Part 2 - Using the new Elasticsearch Java Client](https://spinscale.de/posts/2022-03-03-running-the-elasticcc-platform-part-2.html)  
+  *Blog post, March 2022*
+
+
+* The new Elasticsearch Java Client: getting started and behind the scenes - [Video](https://www.youtube.com/watch?v=61MQoSFt2j0&list=PL_mJOmq4zsHbigQnsjEcWed6N7Do5kss_&index=12), [Slides](https://docs.google.com/presentation/d/1R9pLrRdIPQplNr23TTqST-892Un9g_3AmrLjG5lNM74/present)  
+  *Presentation at the Elastic Community Conference, Feb 2022*