Important information from the deprecated GreenHopper FAQ needs to be included in the main docs

The deprecated GreenHopper FAQ has the following information:

Which fields are required for GreenHopper to be efficient?

The required fields for GreenHopper to be efficient are:
1. The fix version and components, otherwise the planning board would not make any sense.
2. The status of the issue, otherwise the task board would not make any sense.

This should be included in the main documentation. In particular, it should emphasise that a custom field cannot be used in place of these fields.