update docstring

Author: raj454raj

modules/sites/atcoder.py

@@ -79,6 +79,9 @@ def get_problem_setters():
     @staticmethod
     def get_editorial_link(problem_link):
         """
+            @param problem_link (String): Problem URL
+
+            @return (String/None): Editorial link
         """
         try:
             contest_id = re.search("contests/.*/tasks",