Add a doco file since the MaterialOutputAciton is now registered to a…

… syntax

framework/doc/content/source/actions/MaterialOutputAction.md

@@ -0,0 +1,9 @@
+# MaterialOutputAction
+
+!syntax description /Outputs/MaterialOutputAction
+
+This [Action.md] is used to output the material properties computed by a [Material](syntax/Materials/index.md)
+or a [FunctorMaterial](syntax/FunctorMaterials/index.md) to an auxiliary variable.
+Vector, tensor, and array-valued properties can be output to variables prefixed with the component or index.
+
+!syntax parameters /Outputs/MaterialOutputAction

framework/src/actions/MaterialOutputAction.C

@@ -31,6 +31,8 @@ InputParameters
 MaterialOutputAction::validParams()
 {
   InputParameters params = Action::validParams();
+  params.addClassDescription("Outputs material properties to various Outputs objects, based on the "
+                             "parameters set in each Material");
   /// A flag to tell this action whether or not to print the unsupported properties
   /// Note: A derived class can set this to false, override materialOutput and output
   ///       a particular property that is not supported by this class.