Update pulsar-client-cpp README.mc
*Motivation*
There is a error when execute cmake on pulsar-client-cpp
CMake Error at CMakeLists.txt:151 (MESSAGE):
Could not find Boost Python library
@@ -132,6 +132,7 @@ export OPENSSL_ROOT_DIR=/usr/local/opt/openssl/
# For Protobuf
brew install protobuf boost boost-python log4cxx jsoncpp
+// If you are using python3, you need to install boost-python3
# For gtest
cd $HOME
