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.
Okay, I'll see about adding something in that breaks down each of the bits of the `rails` command so that it can (hopefully) make sense.