intro paragraph (#456)

porting/introduction/index.rst

@@ -1,6 +1,12 @@
 Introduction
 ============
 
+Porting is the process of making Ubuntu Touch run on new hardware, i.e. on devices that have not previously been able to run Ubuntu Touch. 
+
+On the vast majority of commercially available devices crucial parts of their systems are not open source. Furthermore, these proprietary parts are specific, not only to the manufacturer, but usually also to the individual model. 
+
+Porting Ubuntu Touch involves building it in such a way as to integrate it with these proprietary components on a device so as to enable it to "talk to" the device hardware. 
+
 Before attempting to port Ubuntu Touch to a new device, there are a few things to understand and consider, some research to be done, and a suitable build environment needs to be set up. This section addresses these points.
 
 .. toctree::
@@ -9,4 +15,4 @@ Before attempting to port Ubuntu Touch to a new device, there are a few things t
 
    Intro
    Preparations
-   Setting_up
+   Setting_up