organizing Markdown syntax of readme.md file

The `readme.md` uses the Markdown syntax in a way that is difficult to read from a code editor, the window that every programmer spend most of their working hours. I've just reformatted the file to serve as base template to document new Drupal projects.

Also, the old formatting left some issues when making item lists without intent properly, like having Markdown plugins unable to render the resulting HTML properly. Those typos was fixed.