Added installation instructions for Ubuntu Linux

Author: daisylb

docs/starting/installation.rst

@@ -121,6 +121,17 @@ To install pip, simply run: ::
 Linux (Ubuntu)
 ::::::::::::::
 
+Natty Narwhal, the latest version of Ubuntu, comes with Python 2.7 out of the box. Python 3.0 can be installed and run with the following commands::
+
+    sudo apt-get install python3-minimal
+    python3
+
+Older versions of Python aren't available from the official repository. However, if it's needed (for example to support legacy code), we can add an unsupported repository and install an older version of Python (2.5 in the example below)::
+
+    $ sudo add-apt-repository ppa:fkrull/deadsnakes
+    $ sudo apt-get update
+    $ sudo apt-get install python2.5
+
 
 
 Linux (Manual)