docs: add fn main to root examples

This is not strictly required, but makes the examples a bit easier to
read understand (especially since the `EventLoop` really _should_ be
created inside `fn main`, and not in some random function potentially
running on a random thread).

src/lib.rs

@@ -7,7 +7,12 @@
 //!
 //! ```no_run
 //! use winit::event_loop::EventLoop;
+//!
+//! # // Intentionally use `fn main` for clarity
+//! fn main() {
 //!     let event_loop = EventLoop::new().unwrap();
+//!     // ...
+//! }
 //! ```
 //!
 //! Then you create a [`Window`] with [`create_window`].
@@ -84,6 +89,8 @@
 //!     }
 //! }
 //!
+//! # // Intentionally use `fn main` for clarity
+//! fn main() {
 //!     let event_loop = EventLoop::new().unwrap();
 //!
 //!     // ControlFlow::Poll continuously runs the event loop, even if the OS hasn't
@@ -97,6 +104,7 @@
 //!
 //!     let mut app = App::default();
 //!     event_loop.run_app(&mut app);
+//! }
 //! ```
 //!
 //! [`WindowEvent`] has a [`WindowId`] member. In multi-window environments, it should be