Add basic installation documentation

Change-Id: Ie656aa1591a9f7aa46bf50714589304cd3196b68

doc/source/index.rst

@@ -6,6 +6,7 @@ Table of Contents
 =================
 
 .. toctree::
-    :maxdepth: 3
+    :maxdepth: 2
 
+    Installing ara-server <installing>
     Architecture and workflows <arch>

doc/source/installing.rst

@@ -0,0 +1,18 @@
+.. _installing:
+
+Installing ara-server
+=====================
+
+``ara-server`` requires a Linux distribution with python 3 in order to work.
+
+It is recommended to use a python `virtual environment <https://docs.python.org/3/tutorial/venv.html>`_
+in order to avoid conflicts with your Linux distribution python packages::
+
+    # Create a virtual environment
+    python3 -m venv ~/.ara/venv
+
+    # Install ara-server from source
+    ~/.ara/venv/bin/pip install git+https://git.openstack.org/openstack/ara-server
+
+    # or install it from PyPi
+    ~/.ara/venv/bin/pip install ara-server