[JIRA] Update jira.issue_worklog() docstring (#580)

Include the required formatting for the parameter `started`

Author: gshel

atlassian/jira.py

@@ -598,7 +598,7 @@ def issue_worklog(self, key, started, time_sec, comment=None):
         """
         :param key:
         :param time_sec: int: second
-        :param started:
+        :param started: str: format ``%Y-%m-%dT%H:%M:%S.000+0000%z``
         :param comment:
         :return:
         """