```ruby
require 'formula'

class Chgems < Formula

  url 'https://github.com/downloads/postmodern/chgems/chgems-0.2.4.tar.gz'
  homepage 'https://github.com/postmodern/chgems#readme'
  md5 '51fd2c6021d95495d41f3a2c4594ccc3'
  head 'https://github.com/postmodern/chgems.git'

  def install
    system 'make', 'install', "PREFIX=#{prefix}"
  end

end
```

Use sha1 instead of md5 (deprecated).
user
```ruby
require 'formula'

class Chgems < Formula

  url 'https://github.com/downloads/postmodern/chgems/chgems-0.2.4.tar.gz'
  homepage 'https://github.com/postmodern/chgems#readme'
  sha1 '12346202c21f0b0ecb91cb9f74abd10ab3fc5384'
  head 'https://github.com/postmodern/chgems.git'

  def install
    system 'make', 'install', "PREFIX=#{prefix}"
  end

end
```
assistant