[globalisel][docs] Add the tutorial to the Porting document

In lieu of converting that tutorial to text, add a link to the porting
tutorial from the 2017 Dev Meeting to the porting page

diff --git a/llvm/docs/GlobalISel/Porting.rst b/llvm/docs/GlobalISel/Porting.rst
index 32ca139..0bc5e74 100644 (file)
--- a/llvm/docs/GlobalISel/Porting.rst
+++ b/llvm/docs/GlobalISel/Porting.rst
@@ -19,3 +19,10 @@ Additionally:
 
 * ``TargetPassConfig`` --- create the passes constituting the pipeline,
   including additional passes not included in the :ref:`pipeline`.
+
+Tutorials
+=========
+
+We'd recommend watching `this tutorial
+<https://www.llvm.org/devmtg/2017-10/#tutorial2>`_ from the 2017 LLVM DevMeeting
+which gave an overview of how to bring up a new backend in GlobalISel.