Document how to connect to xero

[grischard]

The documentation currently says:

When you register your public application with Xero, you'll be given a Consumer Key and a Consumer secret.

That link doesn't load; I get a "Not Authorized." error.

[freakboy3742]

It looks like the documentation has moved; from a quick look, it appears that the link is now here: https://developer.xero.com/documentation/guides/oauth2/auth-flow