How to install avro under ruby?

My OS is CentOS and ruby is 2.1, I want to use avro under ruby, like follows:
the file generate.rb is follows:
require 'rubygems'
require 'avro'
.........

so I download avro-1.7.6.gem and avro-src-1.7.6.tar.gz, but I don't know how to install avro under ruby. Anyone could give me a details command of installing avro under ruby?
Thanks.