Update parameters.rst (#298)

* Update parameters.rst

Make as explicit as possible that if you run with PGEN, then just comment out the global.parameters block in your YAML spec file.

* Update parameters.rst

* Update parameters.rst

* Update parameters.rst

Made changes according to Francesco DiNatale's suggestion.

docs/source/parameters.rst

@@ -52,7 +52,10 @@ Defining multiple parameters in the parameter block will share a 1:1 mapping. Ma
 
   * ...
 
-Maestro does not do any additional operations on parameters such as cross products. If more complex methodologies are required to define parameters then the use of Maestro's :ref:`pgen_section` is recommended.
+Maestro does not do any additional operations on parameters such as Cartesian products. If more complex methodologies are required to define parameters then the use of Maestro's :ref:`pgen_section` is recommended.
+
+.. note
+   Even when using the pgen functionality from the command line, Maestro will still initially verify that the provided specification is valid as if it planned to use it entirely (without pgen). If you are using the ``global.parameters`` block solely as documentation, we recommend that you comment out the ``global.parameters`` block. This lets the validator ignore it.
 
 Defined parameters can be used in steps directly: