[Documentation] Update Discord FAQ

[gabrc52]

I'm filing under bug, since I'm limited to only filing bugs and feature requests.

I'd add a new question:

Q: Messages being sent to the wrong channel

A: You're using webhooks; and the webhook editing functionality is currently broken (#1296). You should move the webhook to the right channel, and make a webhook per channel.

And remove the following question:

Q: Messages not being edited, but a new message with (edit) appears?

Message editing is not supported by discord using webhooks. If you want message editing, disable webhooks and use token only

Since message editing with webhooks is supported and works fine, this should be removed.

I can submit these changes as pull request, if they're okay as in this issue or there's a suggestion to rephrase it.

[gabrc52]

https://github.com/42wim/matterbridge/wiki/Section-Discord-%28basic%29 should be updated as well since webhook editing doesn't work even if the bot has the required permissions.

[qaisjp]

How do your plans change with the introduction of #1323?