That patch does not include the `--with-system-v8` option, which was required for me, as the gem failed to build v8 using what comes with the gem.

A quick look at the documentation shows that bundler does not really support passing options in the Gemfile, and we'd need to use `bundle config` instead.

I think putting it in the Gemfile is a good idea because it locks everybody to the same version, but we still need some instructions in the setup.