Add service reference card

SUMMARY.md

@@ -10,3 +10,4 @@
 * [Quick deployment](doc/quick-deployment.md)
 * [Using Onedock](doc/using-onedock.md)    
 * [Advanced usage](doc/advanced.md)    
+* [Service reference](doc/service-reference.md)   

doc/service-reference.md

@@ -0,0 +1,33 @@
+# ONEDock - Service Reference Card
+
+**Functional description:**  
+  * ONEDock is a set of extensions for [OpenNebula](http://www.opennebula.org/) to use containers as if they were virtual machines (VM).  
+  The concept of ONEDock is to configure Docker to act as an hypervisor. It behaves just as KVM does in the context of OpenNebula.
+
+**Services running:**
+  * ONEDock doesn't start a service on its own and depends on OpenNebula and Docker to work.
+
+
+**Configuration:**
+  * Once ONEDock is installed you could adjust the configuration variables in `/var/lib/one/remotes/onedock.conf` according to your deployment. In particular:
+
+    * LOCAL_SERVER: points to the local docker registry
+    * DATASTORE_DATA_PATH: points to the folder in which the images in the docker registry are stored
+
+**Logfile locations (and management) and other useful audit information:**
+   * *ONEDock log:* The log file is defined in the ONEDOCK_LOGFILE variable of the `/var/lib/one/remotes/onedock.conf` file. The default value is `/var/log/onedock.log`.
+
+**Open ports needed:**
+  * No extra ports are needed by ONEDock although the ports used by OpenNebula and Docker to work properly should be opened.
+
+**Where is service state held (and can it be rebuilt):**  
+  * ONEDock doesn't start a service so there is no service state held.
+
+**Cron jobs:**
+  * None
+
+**Security information**
+   * ONEDock doesn't have any extra security configuration.
+
+**Location of reference documentation:**
+  * [ONEDock on Gitbook](https://indigo-dc.gitbooks.io/onedock/content/)