Change source_suffix type (it should be a dict)

docs/conf.py

@@ -37,11 +37,10 @@ extensions = [
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
 
-# The suffix(es) of source filenames.
-# You can specify multiple suffix as a list of string:
-#
-# source_suffix = ['.rst', '.md']
-source_suffix = '.rst'
+source_suffix = {
+    '.rst': 'restructuredtext',
+    '.md': 'markdown',
+}
 
 # The master toctree document.
 master_doc = 'index'