Add launcher icons section to Exporting for Android. (#3083)

getting_started/workflow/export/exporting_for_android.rst

@@ -60,6 +60,28 @@ In that screen, the path to 3 files needs to be set:
 
 Once that is configured, everything is ready to export to Android!
 
+Providing launcher icons
+------------------------
+
+Launcher icons are used by Android launcher apps to represent your application to users. Godot only requires high-resolution icons (for ``xxxhdpi`` density screens) and will automatically generate lower-resolution variants.
+
+There are two types of icons required by Godot:
+
+- **Main Icon:**: The "classic" icon. This will be used on all Android versions up to Android 8 (Oreo), exclusive. Must be at least 192×192 px.
+- **Adaptive Icons:** Starting from Android 8 (inclusive), `Adaptive Icons <https://developer.android.com/guide/practices/ui_guidelines/icon_design_adaptive>`_ were introduced. Applications will need to include separate background and foreground icons to have a native look. The user's launcher application will control the icon's animation and masking. Must be at least 432×432 px.
+
+.. seealso:: It's important to adhere to some rules when designing adaptive icons. `Google Design has provided a nice article <https://medium.com/google-design/designing-adaptive-icons-515af294c783>`_ that helps to understand those rules and some of the capabilities of adaptive icons.
+
+.. caution:: The most important adaptive icon design rule is to have your icon critical elements inside the safe zone: a centered circle with a radius of 66dp (264 pixels on ``xxxhdpi``) to avoid being clipped by the launcher.
+
+If you don't provide some of the requested icons, Godot will replace them using a fallback chain, trying the next in line when the current one fails:
+
+- **Main Icon:** Provided main icon -> Project icon -> Default Godot main icon.
+- **Adaptive Icon Foreground:** Provided foreground icon -> Provided main icon -> Project icon -> Default Godot foreground icon.
+- **Adaptive Icon Background:** Provided background icon -> Default Godot background icon.
+
+It's highly recommended to provide all of the requested icons, and at least with the specified resolutions. Only this way your application will look great on all the Android devices and versions.
+
 Exporting for Google Play Store
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