STYLE: add notes to some (most) command-line options

- mapFields and splitMeshRegions need more clarification

applications/utilities/mesh/manipulation/setSet/setSet.C

@@ -828,7 +828,12 @@ int main(int argc, char *argv[])
 #   include "addRegionOption.H"
     argList::addBoolOption("noVTK", "do not write VTK files");
     argList::addBoolOption("loop", "execute batch commands for all timesteps");
-    argList::addOption("batch", "file");
+    argList::addOption
+    (
+        "batch",
+        "file",
+        "process in batch mode, using input from specified file"
+    );
 
 #   include "setRootCase.H"
 #   include "createTime.H"