Document elasticsearch data volume

elasticsearch/README.md

@@ -34,6 +34,12 @@ via a volume mounted at `/usr/share/elasticsearch/config`:
 
     docker run -d -v "$PWD/config":/usr/share/elasticsearch/config elasticsearch
 
+This image is configured with a volume at `/usr/share/elasticsearch/data` to
+hold the persisted index data. Use that path if you would like to keep the data
+in a mounted volume:
+
+    docker run -d -v "$PWD/esdata":/usr/share/elasticsearch/data elasticsearch
+
 # License
 
 View license information for [Elasticsearch](http://www.elasticsearch.org/guide/en/elasticsearch/hadoop/current/license.html) software contained in this image.

elasticsearch/content.md

@@ -23,3 +23,9 @@ but if you want to provide your own set of configuration files, you can do so
 via a volume mounted at `/usr/share/elasticsearch/config`:
 
     docker run -d -v "$PWD/config":/usr/share/elasticsearch/config elasticsearch
+
+This image is configured with a volume at `/usr/share/elasticsearch/data` to
+hold the persisted index data. Use that path if you would like to keep the data
+in a mounted volume:
+
+    docker run -d -v "$PWD/esdata":/usr/share/elasticsearch/data elasticsearch