More detail about __WRL_CONFIGURATION_LEGACY__

This adds clarification to exactly what __WRL_CONFIGURATION_LEGACY__  changes.

Author: BenJKuhn

docs/windows/runtimeclass-class.md

@@ -103,7 +103,7 @@ class RuntimeClass<RuntimeClassFlags<classFlags>, I0, I1, I2, I3, I4, I5, I6, I7
  The ninth interface ID. (Optional)  
 
  `classFlags`  
- A combination of one or more [RuntimeClassType](../windows/runtimeclasstype-enumeration.md) enumeration values.  
+ A combination of one or more [RuntimeClassType](../windows/runtimeclasstype-enumeration.md) enumeration values.  The   `__WRL_CONFIGURATION_LEGACY__` macro can be defined to change the default value of classFlags for all runtime classes in the project. If defined, RuntimeClass instances are non-agile dy default. When not defined, RuntimeClass instances are agile by default.
 
 ## Members  
 
@@ -141,4 +141,4 @@ class RuntimeClass<RuntimeClassFlags<classFlags>, I0, I1, I2, I3, I4, I5, I6, I7
  **Namespace:** Microsoft::WRL  
 
 ## See Also  
- [Microsoft::WRL Namespace](../windows/microsoft-wrl-namespace.md)
+ [Microsoft::WRL Namespace](../windows/microsoft-wrl-namespace.md)