Update docker-compose sample file to use local volume driver so data (#4937)

persists even after Minio container is stopped/deleted

docs/orchestration/docker-compose/docker-compose.yaml

@@ -5,7 +5,9 @@ version: '2'
 # 9001 through 9004.
 services:
  minio1:
-    image: minio/minio:RELEASE.2017-08-05T00-00-53Z
+  image: minio/minio
+  volumes:
+   - data1:/data
   ports:
    - "9001:9000"
   environment:
@@ -13,7 +15,9 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio2:
-    image: minio/minio:RELEASE.2017-08-05T00-00-53Z
+  image: minio/minio
+  volumes:
+   - data2:/data
   ports:
    - "9002:9000"
   environment:
@@ -21,7 +25,9 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio3:
-    image: minio/minio:RELEASE.2017-08-05T00-00-53Z
+  image: minio/minio
+  volumes:
+   - data3:/data
   ports:
    - "9003:9000"
   environment:
@@ -29,10 +35,21 @@ services:
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
  minio4:
-    image: minio/minio:RELEASE.2017-08-05T00-00-53Z
+  image: minio/minio
+  volumes:
+   - data4:/data
   ports:
    - "9004:9000"
   environment:
    MINIO_ACCESS_KEY: minio
    MINIO_SECRET_KEY: minio123
   command: server http://minio1/data http://minio2/data http://minio3/data http://minio4/data 
+
+## By default this config uses default local driver,
+## For custom volumes replace with volume driver configuration.
+volumes:
+  data1:
+  data2:
+  data3:
+  data4:
+