[cxx-interop] Clarify the list of supported features

Author: egorzhdan

documentation/cxx-interop/status/index.md

@@ -241,7 +241,7 @@ type can be represented in C++ only when:
 
 - it is a supported Swift structure / class / enumeration that is defined
   in the same Swift module.
-- or, it is a C++ structure, class or enumeration.
+- or, it is a C++ structure / class / enumeration that is not annotated as a reference type.
 - or, it is one of the
   [supported Swift standard library types](#supported-swift-standard-library-types).
   - if it's a generic type, like `Array`, its generic parameters must be bound
@@ -287,6 +287,8 @@ For more details on using Swift types like `String` in C++, check out
 the section that describes how to
 [use Swift standard library types from C++](/documentation/cxx-interop#using-swift-standard-library-types-from-c).
 
+Note that Swift tuples are not currently supported in C++.
+
 ### List Of Primitive Swift Types Supported by C++
 
 This table lists the primitive Swift types defined in Swift's