readme: Move index page content to README

Move the introduction content from the index.rst to the README.rst so
that it can also be found quickly from the top level.

Include the README.rst directly into the index.rst to continue serving
it as the front page material.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

README.rst

@@ -4,6 +4,23 @@
 
 **A complex camera support library for Linux, Android, and ChromeOS**
 
+Cameras are complex devices that need heavy hardware image processing
+operations. Control of the processing is based on advanced algorithms that must
+run on a programmable processor. This has traditionally been implemented in a
+dedicated MCU in the camera, but in embedded devices algorithms have been moved
+to the main CPU to save cost. Blurring the boundary between camera devices and
+Linux often left the user with no other option than a vendor-specific
+closed-source solution.
+
+To address this problem the Linux media community has very recently started
+collaboration with the industry to develop a camera stack that will be
+open-source-friendly while still protecting vendor core IP. libcamera was born
+out of that collaboration and will offer modern camera support to Linux-based
+systems, including traditional Linux distributions, ChromeOS and Android.
+
+Getting Started
+---------------
+
 To build and install:
 
 ::