add mini tutorial about the elasticsearch integration in ReadMe

hapi-fhir-jpaserver-example/README.md

@@ -41,3 +41,17 @@ Use this command to start the container:
   `docker run -d --name hapi-fhir-jpaserver-example -p 8080:8080 hapi-fhir/hapi-fhir-jpaserver-example`
 
 Note: with this command data is persisted across container restarts, but not after removal of the container. Use a docker volume mapping on /var/lib/jetty/target to achieve this.
+
+#### Using ElasticSearch as the search engine instead of the default Apache Lucene
+1. Install ElasticSearch server and the phonetic plugin
+    * Download ElasticSearch from https://www.elastic.co/downloads/elasticsearch
+    * ```cd {your elasticsearch directory}```
+    * ```bin/plugin install analysis-phonetic```
+    * start ElasticSearch server: ```./bin/elasticsearch```
+2. Replace configuration in web.xml
+    * replace the configuration class ```ca.uhn.fhir.jpa.demo.FhirServerConfig``` in web.xml by ```ca.uhn.fhir.jpa.demo.elasticsearch.FhirServerConfig```
+3. Start server by runing: ```mvn jetty:run```
+4. Limitations:
+    * Hibernate search are not compatible with all ElasticSearch version. If you are using Hibernate search: 5.6 or 5.7, the compatible ElasticSearch version is 2.0 - 2.4. If you are using Hibernate search: 5.8 or 5.9, the compatible ElasticSearch version is
+    2.0 - 5.6.
+    * Please check all the limitations in the reference documentation: https://docs.jboss.org/hibernate/search/5.7/reference/en-US/html_single/#elasticsearch-limitations before use the integration.