Mention that format! does not take ownership?

[carols10cents]

In feedback from fbstj:

in the first example of concatenation there was an aside about String + &str taking ownership of
the first part (which might be an extra point against doing the multiple + given potential
precedence oddities) but there's nothing about how format! takes & (I went and looked it up in
the docs/code

basically it's because ownership is brought up during the previous example but not during this it
just felt a little strange.

This feedback is about this paragraph in ch08-02-strings.md:

This code will also set s to "tic-tac-toe". The format! macro works in the same way as println!,
but instead of printing the output to the screen, it returns a String with the contents. This
version is much easier to read than all of the +s.

[fbstj]

OK you mentioned that the book has previously discussed println!. I haven't actually read all the book recently, so reading through this chapter on it's own, this definitely jumped out at me as a question. It might be that readers of the actual book will not hit this since they'll have probably read the previous chapters...