message: Update `counter` example in `README` :tada:
diff: @@ -98,15 +98,9 @@ that can be incremented and decremented using two buttons.
  We start by modelling the __state__ of our application:
  ```rust
  -use iced::button;
  -
  struct Counter {
  // The counter value
  value: i32,
  -
  - // The local state of the two buttons
  - increment_button: button::State,
  - decrement_button: button::State,
  }
  ```
  @@ -125,28 +119,23 @@ Now, let's show the actual counter by putting it all together in our
  __view logic__:
  ```rust
  -use iced::{Button, Column, Text};
  +use iced::widget::{button, column, text, Column};
  impl Counter {
  - pub fn view(&mut self) -> Column<Message> {
  + pub fn view(&self) -> Column<Message> {
  // We use a column: a simple vertical layout
  - Column::new()
  - .push(
  + column![
  // The increment button. We tell it to produce an
  // `IncrementPressed` message when pressed
  - Button::new(&mut self.increment_button, Text::new("+"))
  - .on_press(Message::IncrementPressed),
  - )
  - .push(
  + button("+").on_press(Message::IncrementPressed),
  +
  // We show the value of the counter here
  - Text::new(self.value.to_string()).size(50),
  - )
  - .push(
  + text(self.value).size(50),
  +
  // The decrement button. We tell it to produce a
  // `DecrementPressed` message when pressed
  - Button::new(&mut self.decrement_button, Text::new("-"))
  - .on_press(Message::DecrementPressed),
  - )
  + button("-").on_press(Message::DecrementPressed),
  + ]
  }
  }
  ```
  