Add default prefix

[glen3b]

For a more intuitive experience.

[Wanjiaa]

How does one even call the bot?

[glen3b]

It should send a message with instructions upon joining your server; if it does not, that's a bug.

It is invoked with an @mention prefix by default, including a command which allows you to set the prefix (@CyberScores admin prefix set <prefix here>).