Add helpful text to bot's `sendMoney` response

How to use sendMoney isn't really all that clear. At minimum, should probably:

• Have the bot say "check ur dm" or something like that so the user knows to check their DM for the link
• Add some instructional text to the user's DM that makes it clear the user needs to click the link to send the tx

However, we might also want to somehow have the bot react to the message containing the link or delete it or send another message or some other way of letting the user know not to click old links in the user's DM with the bot and replay attack themselves. This may very well belong in a different issue, as a generic replay-attack defense mechanism for applications like the discord bot that don't have access to the user's keys would be really nice.