Improve event handler doc (#6124)

Author: MetRonnie

cylc/flow/cfgspec/workflow.py

@@ -413,9 +413,10 @@ def get_script_common_text(this: str, example: Optional[str] = None):
                            {item} = echo %(workflow)s
 
                            # configure multiple event handlers
+                           # (which will run in parallel)
                            {item} = \\
-                               'echo %(workflow)s, %(event)s', \\
-                               'my_exe %(event)s %(message)s' \\
+                               'echo %(workflow)s %(event)s', \\
+                               'my_exe %(event)s %(message)s', \\
                                'curl -X PUT -d event=%(event)s host:port'
                     ''')
                 elif item.startswith("abort on"):