Updated v2_0_cpp_adaptor (markdown)

v2_0_cpp_adaptor.md

@@ -39,8 +39,8 @@ msgpack-c provides predefined adaptors for C++ primitive types and standard libr
 | array_ref *3      | array                       |since 1.2.0|
 | raw_ref *3        | bin                         |    |
 | v4raw_ref *3      | str                         |since 1.2.0|
-| ext               | ext                         |    |
-| ext_ref *3        | ext                         |    |
+| ext               | ext                         |*4    |
+| ext_ref *3        | ext                         |*4   |
 | variant           | any type                    |since 1.2.0, boost is required|
 
 | C++11 type         | msgpack::object type        |note|
@@ -73,6 +73,9 @@ unsigned char, unsigned short, unsigned int, signed long, signed long long
 *3 xxx_ref types
 enforce packing types without copies.
 
+*4 ext with maximum size limitation
+On 64bit environment, there is no limitation. But on 32bit environment, ext32 with maximum size is not supported. See https://github.com/msgpack/msgpack-c/pull/175#issue-51915694
+
 msgpack::object type is defined as follows:
 https://github.com/msgpack/msgpack/blob/master/spec.md