DOCU: inconsistent documentation for pressure FO

Header file mentions keywords pRef optional with default value = 0.

However, this becomes compulsory with dictLookup entry.

Should either be modified to make it consistent (or state conditions when it is required)?

Property     | Description                 | Required                    | Default value
pRef         | Reference pressure          | for total pressure          | 0
pInf         | Freestream pressure         | for coefficient calculation |