Use argList::addOption, argList::addBoolOption (almost) everywhere

- ensure that the standard options (eg, from timeSelector) also have
  some usage information

applications/solvers/basic/potentialFoam/potentialFoam.C

@@ -38,11 +38,9 @@ Description
 
 int main(int argc, char *argv[])
 {
-
-    argList::validOptions.insert("writep", "");
+    argList::addBoolOption("writep", "write the final pressure field");
 
 #   include "setRootCase.H"
-
 #   include "createTime.H"
 #   include "createMesh.H"
 #   include "createFields.H"