Create empty string and grow it using push and push_str

---

examples/strings/create-empty-string/src/main.rs

fn main() {
    let mut text = String::new();
    println!("{text:?}");

    text.push_str("Hello");
    println!("{text:?}");

    text.push(' ');
    println!("{text:?}");

    text.push_str("World");
    println!("{text:?}");

    text.push('!');
    println!("{text:?}");
}

""
"Hello"
"Hello "
"Hello World"
"Hello World!"