backend: update comment for MarkAllTodos to indicate status variable

Author: kahkeng

backend/schema.py

@@ -153,7 +153,7 @@ def mutate_and_get_payload(cls, root, info, **input):
 
 
 class MarkAllTodos(relay.ClientIDMutation):
-    # mutation MarkAllTodosMutation($input: MarkAllTodosInput!) {
+    # mutation MarkAllTodosMutation($input: MarkAllTodosInput!, $status: String!) {
     #   markAllTodos(input: $input) {
     #     changedTodos { id complete }
     #     viewer { id completedCount }