Add link to documentation when using forbidden arguments in register

What does this MR do?

This MR adds a link to the documentation that explains which arguments are forbidden when using a runner authentication token.

Why was this MR needed?

Because it is not obvious to users which arguments are disallowed when they are faced with this error.

What's the best way to test this MR?

Run the following command:

gitlab-runner register  --url http://gdk.test:3000  --token glrt-fake-token --run-untagged --executor shell --non-interactive

What are the relevant issue numbers?

N/A. See https://gitlab.slack.com/archives/CBQ76ND6W/p1689362509429609 (internal)