Enable sphinx_design extension in conf.py

Author: jsiegle

source/conf.py

@@ -41,7 +41,8 @@
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = ["sphinx.ext.todo", 
-              "sphinx.ext.githubpages"]
+              "sphinx.ext.githubpages",
+              "sphinx_design"]
 
 
 # Add any paths that contain templates here, relative to this directory.