Getting started edits

These two proposed edits are based upon feedback I've gotten from participants:

- I've often been asked what `-T` means when generating the Rails app
- I've often been asked what `g` meant in the rails command and why `body` needs a data type but `title` does not.
Types are an issue with new developers so I expect that some would find this confusing, but I can't think of a better way to solve the problem.