ENH: mapFields: improved comment

applications/utilities/preProcessing/mapFields/mapFieldsDict

@@ -14,6 +14,12 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+// Specify how to map patches. There are three different options:
+// - patch exists in the source case: specify mapping (patchMap)
+// - patch should be interpolated from internal values in source case
+//   (cuttingPatches)
+// - patch should not be mapped. Default if not in patchMap or cuttingPatches
+
 // List of pairs of target/source patches for mapping
 patchMap
 (