Fixes for the bot mentions

[etspaceman]

When I was testing this out, I noticed a couple of things:

• Bots were not included in the mentions for a message
• Message Content is a special privilege that needed to be added

Added a section about this in the README and leveraged the message content instead of the mentions.

[internetisgone]

message content intent is not required in order for the bot to see content of messages that mention it. i think it's good practice to give the bot only the minimal required permissions. interaction was changed from ! command prefix to @ mentions for this very reason c81096a

[etspaceman]

When I was testing this out on my own servers, mentioning a bot user specifically did not show up in the mentions for a message. So I had to resort to using message content.

We ended up making a new update that leverages a role instead of the user though. That is because it was not possible to restrict the use of the bot for users. Having the bot be a part of a role that is referenced does allow for that. And it shows up in role_mentions. Something to think about with this repo.