Update userguide .mod files: add comment to match text of userguide

(cherry picked from commit 15d4e8b8)

doc/userguide/models/fs2000ns.mod

@@ -63,6 +63,10 @@ y = 0.6;
 dA = exp(gam);
 end;
 
+// the above is really only useful if you want to do a stoch_simul
+// of your model, since the estimation will use the Matlab
+// steady state file also provided and discussed above.
+
 steady;
 
 estimated_params;