ref(docs): add link to installing Deis

Author: Matthew Fisher

docs/index.rst

@@ -3,11 +3,13 @@
 
 Welcome
 =======
+
 Deis (pronounced DAY-iss) is an open source PaaS that makes it easy to deploy and manage applications
 on your own servers. Deis builds upon Docker and CoreOS to provide a lightweight PaaS with a
 Heroku-inspired workflow.
 
-To get started with Deis, first read :ref:`Understanding Deis <understanding_deis>`.
+To get started with Deis, first read :ref:`Understanding Deis <understanding_deis>` then use
+:ref:`installing_deis` to start provisioning your cluster.
 
 The full documentation tree can be seen :ref:`here <toctree>`.