Add Quobyte volumes in docs

Author: Johannes Scheuermann

docs/user-guide/volumes.md

@@ -71,6 +71,7 @@ Kubernetes supports several types of Volumes:
    * `downwardAPI`
    * `azureFileVolume`
    * `vsphereVirtualDisk`
+   * `Quobyte`
 
 We welcome additional contributions.
 
@@ -477,6 +478,15 @@ spec:
       fsType: ext4
 ```
 
+### Quobyte
+
+A `Quobyte` volume allows an existing [Quobyte](http://www.quobyte.com) volume to be mounted into your pod.
+
+__Important: You must have your own Quobyte setup running with the volumes created
+before you can use it__
+
+See the [Quobyte example](https://github.com/kubernetes/kubernetes/tree/{{page.githubbranch}}/examples/volumes/quobyte) for more details.
+
 ## Resources
 
 The storage media (Disk, SSD, etc) of an `emptyDir` volume is determined by the