In nginx reverse proxy doc, specify the link/port to use in nginx conf

[roxk]

In the nginx reverse proxy doc, the nginx conf is supposed to be configured with the following authgear endpoint:

It doesn't work for locally deployed authgear if the user specified the authgear web page endpoint + port. Nginx would produce obscure error (host not found instead of connection refused).

It'd be great if the doc adds a section saying for locally deployed authgear, instead of using 3000, 3001 should be used instead.