Disabled by default except on development

[jaimeiniesta]

Hi!

Thanks for making this compatible with rails 3. I love it!

I've made a little change, so that on the generated query_reviewer.yml, it sets "enabled=false" for all environments and then it gets overriden to true for development. This way, you can't forget to disable it on other environments like staging or integration, and you only need to change this file if you want to explicitly enable it on some other environments.

Also, I've fixed a small typo and updated the README.

Thanks!