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/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()
     }