Send DM to the author of a potentially inappropriate message

[tk3369]

Related to the whistle blower report function from #34, I want the bot to send a DM to the author of the potentially inappropriate message. Here's what I think the requirements are:

1. The message should be phrased professionally to avoid provoking adverse behavior;
2. The message may contain a link to the the community rules post in #readme;
3. The message may suggest the author to consider editing or removing the content;
4. The message may advise the author to contact the moderators if necessary;