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.
Always happy to kill more jargon.  How about:

"2. if you do not specify what you want your attribute to be (like a `string` or `text`), Rails will just assume you want it to be a `string`"

or, slightly different:

"2. if you do not specify what kind of thing you want your attribute to be (like a `string` or `text`), Rails will just assume you want it to be a `string`"