updated readme install instructions

Author: Thomas Preston

README.md

@@ -12,12 +12,17 @@ Documentation
 Installation
 ============
 
+Download the latest releases of
+[pifacecommon](https://github.com/piface/pifacecommon/releases) and
+[pifacedigitalio](https://github.com/piface/pifacedigitalio/releases).
+Then install with:
+
+    $ dpkg -i python3-pifacecommon_2.0.2-1_all.deb python3-pifacedigitalio_2.0.2-1_all.deb
+
+Or you can install without using your package manager:
+
     $ git clone https://github.com/piface/pifacedigitalio.git
     $ cd pifacedigitalio
     $ sudo python3 setup.py install
 
-For those of you who are still using Python 2:
-
-    $ sudo python setup.py install
-
-You may need to reboot.
+*Replace `python3` for `python` if you're using Python 2.*