[docs] Port FAQ over to Sphinx.

Patch by Mikael Lyngvig!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158677 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/userguides.rst b/docs/userguides.rst
index eb70028..d59ef7f 100644
--- a/docs/userguides.rst
+++ b/docs/userguides.rst
@@ -7,6 +7,7 @@
    :hidden:
 
    CommandGuide/index
+   FAQ
 
 \
 
@@ -45,7 +46,7 @@
 
     A list of optimizations and analyses implemented in LLVM.
     
- * `Frequently Asked Questions <FAQ.html>`_
+ * :ref:`faq`
 
     A list of common questions and problems and their solutions.