update text to explain Discord on profile page

[Raven-St]

Next text should read:

After you have joined the Arisia Discord server, type your Discord account name and the 4 numbers after it (including the pound sign) into the box below and press Submit. Entering your Discord information connects your Discord account to Arisia and allows you full access the Arisia Discord server. If you have not yet joined the server, you can do so by [clicking here].

[clicking here] should be a link to the Discord server.