ENH: consistent handling of "value" for faePatchField

- base level now explicity equivalent to LAZY_READ with overriding as
  required

- clearer documentation for reading of "value" for faPatchField

src/finiteArea/fields/faPatchFields/basic/transform/transformFaPatchField.C

@@ -62,7 +62,7 @@ Foam::transformFaPatchField<Type>::transformFaPatchField
     const dictionary& dict
 )
 :
-    faPatchField<Type>(p, iF, dict)
+    faPatchField<Type>(p, iF, dict, IOobjectOption::NO_READ)
 {}