add utf8 comment

Author: phaustin

jupyter_sphinx/execute.py

@@ -256,7 +256,8 @@ def write_notebook_output(notebook, output_dir, notebook_name):
         resources,
         os.path.join(output_dir, notebook_name + ".ipynb"),
     )
-    # Write a script too.
+    # Write a script too.  Note that utf-8 is the de facto
+    # standard encoding for notebooks. 
     ext = notebook.metadata.language_info.file_extension
     contents = "\n\n".join(cell.source for cell in notebook.cells)
     with open(os.path.join(output_dir, notebook_name + ext), "w",