[docs] Convert docs index page into Sphinx.

- Work in progress, this is mostly important because it lets us incrementally migrate the remaining documentation.
 - Lots of styling, editing, and integration work yet to come…
 - PR12589

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155133 91177308-0d34-0410-b5e6-96231b3b80d8

docs/design_and_overview.rst

@@ -0,0 +1,31 @@
+.. _design_and_overview:
+
+LLVM Design & Overview
+======================
+
+ * `LLVM Language Reference Manual <LangRef.html>`_
+
+   Defines the LLVM intermediate representation.
+
+ * `Introduction to the LLVM Compiler <http://llvm.org/pubs/2008-10-04-ACAT-LLVM-Intro.html>`_
+
+   Presentation providing a users introduction to LLVM.
+
+ * `Intro to LLVM <http://www.aosabook.org/en/llvm.html>`_
+
+   Book chapter providing a compiler hacker's introduction to LLVM.
+
+ * `LLVM: A Compilation Framework forLifelong Program Analysis & Transformation
+   <http://llvm.org/pubs/2004-01-30-CGO-LLVM.html>`_
+
+   Design overview.
+
+ * `LLVM: An Infrastructure for Multi-Stage Optimization
+   <http://llvm.org/pubs/2002-12-LattnerMSThesis.html>`_
+
+   More details (quite old now).
+
+ * `GetElementPtr FAQ <GetElementPtr.html>`_
+
+   Answers to some very frequent questions about LLVM's most frequently
+   misunderstood instruction.