Add warning to config

sample-config.cfg

@@ -35,6 +35,8 @@ monitor = contact@mastodon.example
 # The full names of each account you want to notify when the monitored
 # account gets a notification, separated by a comma (but no space!), 
 # without the initial @.
+# Pingbot does not verify that you have permission to send messages to
+# these accounts, so please use this cautiously.
 notify = admin@mastodon.example,moderator@mastodon.example
 # If this is "True", Pingbot will forward the full message to each
 # account above; if it's anything else, Pingbot will just send a link to