Persist Elasticsearch data by default via named volume (#430)

* Persist Elasticsearch data by default via named volume

* update volume declaration to long format

* Update README

docker-compose.yml

@@ -1,7 +1,6 @@
 version: '3.2'
 
 services:
-
   elasticsearch:
     build:
       context: elasticsearch/
@@ -12,6 +11,9 @@ services:
         source: ./elasticsearch/config/elasticsearch.yml
         target: /usr/share/elasticsearch/config/elasticsearch.yml
         read_only: true
+      - type: volume
+        source: elasticsearch
+        target: /usr/share/elasticsearch/data
     ports:
       - "9200:9200"
       - "9300:9300"
@@ -63,6 +65,8 @@ services:
       - elasticsearch
 
 networks:
-
   elk:
     driver: bridge
+
+volumes:
+  elasticsearch: