Clarify help text

[florianm]

Adding a dataset as "species observation" with a field "name_id", the field apparently is not recognised as Name ID field. Saving the dataset fails with error message:

Schema errors for resource "threatened_fauna_occurrence": The schema doesn't include a 'Species Name' field or a 'Name Id' field. In order to be a valid Species Observation one of these fields must be specified. Alternatively you can 'tag' a field by adding a biosys type: 'speciesName' or 'speciesNameId'

This message leaves unclear where exactly to insert what data into the datapackage config.

The config as inferred from a CSV:

{
            "type": "integer",
            "name": "name_id",
            "format": "default"
          },

This ended up working:

          {
            "type": "integer",
            "name": "name_id",
            "format": "default",
            "constraints": {"required": true},
            "biosys": {"type": "speciesNameId"}
          },

Could the help text include an example on how to "add a biosys type"?