Platform: reference useful APIs and docs from setWindowIcon().

src/Magnum/Platform/GlfwApplication.h

@@ -481,6 +481,8 @@ class GlfwApplication {
          * @note Available since GLFW 3.2. The function has no effect on macOS
          *      / Wayland, see @m_class{m-doc-external} [glfwSetWindowIcon()](https://www.glfw.org/docs/latest/group__window.html#gadd7ccd39fe7a7d1f0904666ae5932dc5)
          *      for more information.
+         * @see @ref platform-windows-icon "Excecutable icon on Windows",
+         *      @ref Trade::IcoImporter "IcoImporter"
          */
         void setWindowIcon(std::initializer_list<ImageView2D> images);
 

src/Magnum/Platform/Sdl2Application.h

@@ -787,6 +787,8 @@ class Sdl2Application {
          *      have no effect on macOS / Wayland, similarly to how
          *      @ref GlfwApplication::setWindowIcon() behaves on those
          *      platforms.
+         * @see @ref platform-windows-icon "Excecutable icon on Windows",
+         *      @ref Trade::IcoImporter "IcoImporter"
          */
         void setWindowIcon(const ImageView2D& image);
         #endif