autotools build needs pkg-config in README.md
autotools build needs pkg-config in README.md

The autotools build needs pkg-config. Add this to the README.md file.
sakishum/rabbitmq-c,soindy/rabbitmq-c,jasonmsoft/rabbitmq-c,jqk6/rabbitmq-c,sakishum/rabbitmq-c,jasonmsoft/rabbitmq-c,jqk6/rabbitmq-c,hjzljp/rabbitmq-c,tempbottle/rabbitmq-c,hjzljp/rabbitmq-c,jqk6/rabbitmq-c,soindy/rabbitmq-c,chenwenbin928/rabbitmq-c,sakishum/rabbitmq-c,alanxz/rabbitmq-c,Haster2004/rabbitmq-c,alanxz/rabbitmq-c,tempbottle/rabbitmq-c,jasonmsoft/rabbitmq-c,hjzljp/rabbitmq-c,Haster2004/rabbitmq-c,Haster2004/rabbitmq-c,tempbottle/rabbitmq-c,chenwenbin928/rabbitmq-c,chenwenbin928/rabbitmq-c,jqk6/rabbitmq-c,jasonmsoft/rabbitmq-c,kilinrax/rabbitmq-c,tempbottle/rabbitmq-c,kilinrax/rabbitmq-c,alanxz/rabbitmq-c,soindy/rabbitmq-c,hjzljp/rabbitmq-c,kilinrax/rabbitmq-c