add ruby dependence to readme
add ruby dependence to readme

uwsampa/grappa,buaasun/grappa,alexfrolov/grappa,alexfrolov/grappa,uwsampa/grappa,buaasun/grappa,buaasun/grappa,alexfrolov/grappa,alexfrolov/grappa,buaasun/grappa,alexfrolov/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,alexfrolov/grappa,uwsampa/grappa,buaasun/grappa,buaasun/grappa,uwsampa/grappa,uwsampa/grappa