Improved Docker examples (#1308)

- Fixed a bug in the persistent docker command ("server" in place of "export")
- Added example of how to set consistent keys with ephemeral data, particularly useful for testing.

Docker.md

@@ -1,13 +1,25 @@
 ### Run Minio docker image
 
-Start docker, however data is not persistent.
+Start docker with random keys, generated name, and ephemeral data:
 
 ```bash
 docker run -p 9000:9000 minio/minio server /export
 ```
 
-Map export and configuration directories from host for persistence.
+Start docker, ephemeral data with consistent name (minio1) and keys (examples shown are from AWS documentation and should be changed):
 
 ```bash
-docker run -p 9000:9000 --name minio1 -v /mnt/export/minio1:/export -v /mnt/config/minio1:/root/.minio minio/minio export /export
+docker run -p 9000:9000 --name minio1 \
+  -e "MINIO_ACCESS_KEY=AKIAIOSFODNN7EXAMPLE" \
+  -e "MINIO_SECRET_KEY=wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY" \
+  minio/minio server /export
+```
+
+Map export and configuration directories from host for persistence:
+
+```bash
+docker run -p 9000:9000 --name minio1 \
+  -v /mnt/export/minio1:/export \
+  -v /mnt/config/minio1:/root/.minio \
+  minio/minio server /export
 ```