If this is something that will be used in multiple schemas, or if the list of allowable values is quite long, also consider uploading a single-column dataset (sometimes known as a List) and reference that in the Type field.
From the Dataset upload page (Mockaroo - New Dataset):
Mockaroo supports two types of data files:
Lists
If your dataset is a simple list of values, specify each value on a separate line. Do not include a header row.
Example:
Ford
Ferrari
Honda
Toyota