Very small typo fix (#3693)

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Small spelling error - changed `Addintional` to `Additional`

crates/eframe/src/epi.rs

@@ -217,7 +217,7 @@ pub enum HardwareAcceleration {
 
 /// Options controlling the behavior of a native window.
 ///
-/// Addintional windows can be opened using (egui viewports)[`egui::viewport`].
+/// Additional windows can be opened using (egui viewports)[`egui::viewport`].
 ///
 /// Set the window title and size using [`Self::viewport`].
 ///