Add FAQ command

[debashisbiswas]

The FAQ command is a new command that will send users information about the channel they send the command in. When a user uses !FAQ in a channel, Horace will

1. delete the command after ~1 second (long enough to let the user know that their message successfully sent)
2. DM the user with the FAQ designated to the specific channel the user sent the command in

This command will only be accessible in the community channels (channels where general users post, so no administrative, announcement, or role-selection channels). The rest of the team is working on writing up the FAQ for each channel - for now, we just need to set up a system to use them when they're available.