ENH: additional feedback about controlled mesh motion update type

- ensure that the updateControl is "non-sticky" on re-read,
  even if we do not support runtime-modifiable here

STYLE: add syntax example (wingMotion), but with updateInterval 1

tutorials/incompressible/pimpleFoam/RAS/wingMotion/wingMotion2D_pimpleFoam/constant/dynamicMeshDict

@@ -20,6 +20,11 @@ motionSolverLibs (sixDoFRigidBodyMotion);
 
 motionSolver    sixDoFRigidBodyMotion;
 
+// Not necessarily useful here, but can have different motion updates types
+updateControl   timeStep;
+updateInterval  1;
+
+
 patches         (wing);
 innerDistance   0.3;
 outerDistance   1;