Re-imagined README.md for rails applications

I think that this is something that would differ incredibly from app to app. For instance, I would not install Ruby using apt-get myself.

While I like the idea of having it be a “Getting Started” doc for an app, I don’t think that Rails could come with a cohesive default that would work for everyone.

-1 to this change.

As a more general comment, if something like this was to be added I think it's important to decide what the expected audience for the README is. For instance, definitions of Rails terms and instructions on how to install Ruby and webservers are probably overkill if the audience is "developers new to the app but not to Rails".

One thing that might be useful - somehow hook into the various choices available in `rails new` (test framework, ORM, etc) and include details in the generated file. So for instance, selecting Rspec would produce a paragraph about how to run the specs.

--Matt Jones