add version explanation

Author: JamesClonk

README.md

@@ -71,20 +71,30 @@ Similarly if no datacenter is configured it will use `aws:eu-central-1` as defau
 When issuing service provisioning requests to the service broker it is possible to provide the account id and/or the datacenter as additional parameters.
 ###### Example:
 ```bash
-$ cf create-service etcd default my-etcd -c '{
+cf create-service etcd default my-etcd -c '{
   "account_id": "454f3deb8cad236ffb3452e9", 
   "datacenter": "gce:europe-west1"
 }'
 ```
 
 #### Units
 
-When issuing service provisioning requests to the service broker it is also possible to request a specific [unit](https://apidocs.compose.com/docs/scaling) size (which basically determines the scaling for your Compose.io deployments, memory and disk space) instead of the configured value in the service brokers `catalog.yml`.
+When issuing service provisioning requests to the service broker it is also possible to request a specific [unit](https://apidocs.compose.com/docs/scaling) size (which basically determines the scaling for your Compose.io deployments, _memory_ and _disk space_) instead of the configured value in the service brokers `catalog.yml`.
 
 It is also possible to update existing service instances with `cf update-service`.
 ###### Example:
 ```bash
-$ cf create-service scylla default my-scylla-db -c '{ "units": 10 }'
+cf create-service scylla default my-scylla-db -c '{ "units": 10 }'
 # or
-$ cf update-service my-postgres-db -c '{ "units": 4 }'
+cf update-service my-postgres-db -c '{ "units": 4 }'
+```
+
+#### Version
+
+Last but not least it is also possible during service provisioning to request specific software versions for your database deployments.
+You can get all available versions from the [Compose.io API](https://apidocs.compose.com/reference#2016-07-get-databases): https://api.compose.io/2016-07/databases
+
+###### Example:
+```bash
+cf create-service rethink default my-rethinkdb -c '{ "version": "2.3.7" }'
 ```