`quote`-compatible example

I think it would be very valuable to have an example in the root documentation showing how to use with the `quote` crate.

Something like this:

```rust
fn main() {
let rust_snippet = quote!{
fn hello_world() {println!("hello world !")}
};

let abstract_file : File = syn::parse2(rust_snippet);
let pretty_rust = prettyplease::unparse(abstract_file);

println!(pretty_rust);
}
```

Start by reading the root documentation and checking how examples and dependencies are currently presented. Add a quote-compatible usage example based on the issue's snippet, then verify that the example matches the documented API and builds or otherwise renders correctly.

Written by the indexing model from the issue text.