Please add instructions on how to debug webhooks

[smaktacular]

Maybe I missed it, but there seems to be no documentation about how to proceed if one configured the webhooks plugin but no POST requests are happening. The logs don't tell anything and the client trace only shows that the auth_on_publish hook is being called. But even the auth_on_publish does not execute any post. As we are using the docker image I guess there is not much that could be set up wrong.

Nevertheless, it seems we missed out on something during the setup of the hooks. If the documentation would show how to debug such issues users could more likely help themselves.