Update property.md

The usage property is required when invoking npm run build on a PCF project.

Author: Eickhel

powerapps-docs/developer/component-framework/manifest-schema-reference/property.md

@@ -28,7 +28,7 @@ Model-driven apps and canvas apps (public preview)
 |name |Name of the property |string |Yes |
 |display-name-key |Used in the customization screens as localized strings that describes the name of the property. |string |Yes |
 |of-type| Defines the data type of the property| See [Remarks](#remarks)|Optional|
-|usage |The usage attribute identifies if the property is meant to represent an entity attribute that the component can change (bound) or read-only values (input)|bound or input |Optional |
+|usage |The usage attribute identifies if the property is meant to represent an entity attribute that the component can change (bound) or read-only values (input)|bound or input |Yes |
 |required |Whether the property is required or not |boolean |Optional |
 |of-type-group |Name of the type-group as defined in manifest| string |Optional |
 |description-key |Used in the customization screens as localized strings that describes the description of the property. |string |Optional |