docs: Add link to external LLVM backend tutorial.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170998 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/tutorial/index.rst b/docs/tutorial/index.rst
index 4658f96..c2ef3b9 100644
--- a/docs/tutorial/index.rst
+++ b/docs/tutorial/index.rst
@@ -22,6 +22,14 @@
 
    OCamlLangImpl*
 
+External Tutorials
+==================
+
+`Write An LLVM Backend Tutorial For Cpu0 <http://jonathan2251.github.com/lbd/>`_
+   A step-by-step tutorial for developing an LLVM backend. Under
+   active development at `<https://github.com/Jonathan2251/lbd>`_ (please
+   contribute!).
+
 
 Advanced Topics
 ===============