Adds doc comment for disabled button

Makes disabled button behavior consistent in web

native/src/widget/button.rs

@@ -29,6 +29,13 @@ use std::hash::Hash;
 /// let button = Button::new(&mut state, Text::new("Press me!"))
 ///     .on_press(Message::ButtonPressed);
 /// ```
+///
+/// Buttons can be disabled by not having an on_press.
+///
+/// ```
+/// let mut state = button::State::new();
+/// let disabled_button = Button::new(&mut state, Text::new("I'm disabled!"));
+/// ```
 #[allow(missing_debug_implementations)]
 pub struct Button<'a, Message, Renderer: self::Renderer> {
     state: &'a mut State,
@@ -97,6 +104,7 @@ where
     }
 
     /// Sets the message that will be produced when the [`Button`] is pressed.
+    /// If on_press isn't set, button will be disabled.
     pub fn on_press(mut self, msg: Message) -> Self {
         self.on_press = Some(msg);
         self