Configuration options and hints

Thx for this plugin.

I've created an issue for the GRAV admin plugin: [Issue](https://github.com/getgrav/grav-plugin-admin/issues/927). This issue affects the popularity counters exposed in the dashboard of the admin plugin. To solve these issues I propose to implement the following:

A hint that makes clear that a personalized error page needs to use specific templates (right now only templates with the name "error" are totally supported)

That's not really a bug but it's important because statistics are important.