Update app.py

updated function

app.py

@@ -13,8 +13,8 @@ def count_string_occurrences(main_string: str, sub_string:str) -> int:
     Returns the number of times sub_string occurs in main_string.
     
     Args:
-        main_string (str): The main string to search in.
-        sub_string (str): The substring to search for.
+        main_string: The main string to search in.
+        sub_string: The substring to search for.
     
     Returns:
         int: The number of occurrences of sub_string in main_string.