enh: update README with new Docker instructions

README.md

@@ -33,16 +33,19 @@ run mongodb://myuser:mypassword@myhost:myport/mydb?mycollection
 You need to have a MongoDB running with the corresponding user declared in the *admin* database (by convention).
 To run a mongoDB using docker (you need to forward the port):
 ```jshelllanguage
-docker pull mongo
-docker run --name some-mongo -p 27017:27017 -d mongo
-```
-Then, create the user (openmole by defaut):
-```jshelllanguage
-mongo
-use admin
-db.createUser({ user: 'openmole', pwd: 'rocks', roles: ["readWrite"  ] })
-use openmole
-db.test.save({a:"b"})
+cd docker
+docker build -t openmole/mongo-gate .
+mkdir -p data/{configdb,db}
+docker run                                 \
+    -v $(pwd)/data/db:/data/db             \
+    -v $(pwd)/data/configdb:/data/configdb \
+    --name openmole-gate-dummy             \
+    -p 27017:27017                         \
+    --restart=always                       \
+    -e MONGO_INITDB_DATABASE=openmole      \
+    -d openmole/mongo-gate:latest
 ```
 
+This will start a MongoDB instance prepopulated with an `openmole` user and a dummy record in a `test` collection.
+
 Then, browse [localhost:8080](localhost:8080)
\ No newline at end of file