added some more info

Author: fahadnayyar

documentation/cxx-interop/index.md

@@ -1259,6 +1259,12 @@ object.doSomething()
 
 When a C++ type inherits from a `SWIFT_SHARED_REFERENCE` base type, the Swift compiler automatically infers `SWIFT_SHARED_REFERENCE` annotation for the derived type.
 The derived type also gets imported as a reference type, and uses the same `retain` and `release` functions as its base class.
+This inference works as long as all the annotated base types in the inheritance chain (including multiple or indirect inheritance) have the same `retain` and `release` functions.
+If multiple base types have conflicting `retain` or `release` functions, the derived type is imported as a Swift value type, and the compiler emits a warning.
+
+
+Note that this inference currently applies only to `SWIFT_SHARED_REFERENCE`. 
+It does not apply to types annotated with `SWIFT_IMMORTAL_REFERENCE` or `SWIFT_UNSAFE_REFERENCE`.
 
 ### Inheritance and Virtual Member Functions