Import README.md into pigweed docs

Replaces the contents of the Pigweed documentation landing page with
the README.md inlined and converted to rst.

Change-Id: I6457aaede5ca4c0585af4a00c388278fb14223f5
diff --git a/docs/index.rst b/docs/index.rst
index 169bdcf..80157ad 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1,16 +1,18 @@
-=======
-Pigweed
-=======
+.. _chapter-home:
 
-Pigweed is a collection of embedded-focused libraries, which we call "modules".
-These modules are designed for small-footprint MMU-less microcontrollers like
-the ST Micro STM32L452 or the Nordic NRF82832. The modules are designed to
-facilitate easy integration into existing codebases.
+.. highlight:: sh
+
+====
+Home
+====
+
+.. mdinclude:: README.md
 
 .. toctree::
   :maxdepth: 1
   :hidden:
 
+  self
   docs/embedded_cpp_guide
   docs/style_guide
   targets