Document Android raw_window_handle requirements (#1749)

* Add docs describing raw_winow_handle on android

* Run cargo fmt

* Change raw_window_handle panic to give more info

src/platform_impl/android/mod.rs

@@ -505,7 +505,7 @@ impl Window {
         let a_native_window = if let Some(native_window) = ndk_glue::native_window().as_ref() {
             unsafe { native_window.ptr().as_mut() as *mut _ as *mut _ }
         } else {
-            panic!("native window null");
+            panic!("Cannot get the native window, it's null and will always be null before Event::Resumed and after Event::Suspended. Make sure you only call this function between those events.");
         };
         let mut handle = raw_window_handle::android::AndroidHandle::empty();
         handle.a_native_window = a_native_window;

src/window.rs

@@ -784,6 +784,12 @@ impl Window {
 }
 
 unsafe impl raw_window_handle::HasRawWindowHandle for Window {
+    /// Returns a `raw_window_handle::RawWindowHandle` for the Window
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Android:** Only available after receiving the Resumed event and before Suspended. *If you*
+    /// *try to get the handle outside of that period, this function will panic*!
     fn raw_window_handle(&self) -> raw_window_handle::RawWindowHandle {
         self.window.raw_window_handle()
     }