add source_suffix sphinx config

Author: JessicaS11

_config.yml

@@ -83,5 +83,6 @@ sphinx:
       scipy-tutorial/00_overview.ipynb: overview/get-started.md
       workshops/scipy2022/README.md: overview/fundamental-path/README.md
       fundamentals/02.1_working_with_labeled_data.ipynb: fundamentals/02.1_indexing_Basic.ipynb
-
+    source_suffix:
+      '.md': 'markdown'
     bibtex_reference_style: author_year # or label, super, \supercite