Add reproduction script that use gems from repos/

[benoittgt]

Hello

I always look at the best way to start contributing to RSpec. I think rspec-dev is full of powerfull rake commands but lack of documentation to properly start hacking RSpec.

The idea here is to have a basic test suite that will use gems from repos/.

If you love the idea I think we can add some doc to contributing guide with for example.

1. git clone https://github.com/rspec/rspec-dev
2. cd rspec-dev && bundle install
3. rake git:clone
4. cd repro-scripts && bundle install
5. bundle exec rspec

Or add a rake task that handle this.