Adds `add_messages` README.md
Adds `add_messages` README.md

cao1998wang/endpoint_base,cao1998wang/endpoint_base,spree/endpoint_base,CasperSleep/endpoint_base,spree/endpoint_base,CasperSleep/endpoint_base,cao1998wang/endpoint_base,spree/endpoint_base,CasperSleep/endpoint_base