Document what showWithEffect and hideWithEffect do when an animation … #736

Job	Run time
ios-sfml-graphics	55s
ios-sdl	3m 14s
android-sfml-graphics	2m 49s
android-sdl	6m 10s
linux	5m 45s
linux-latest-dev	3m 49s
linux-oldest	3m 15s
linux-per-backend	5m 27s
macos	2m 8s
windows	2m 33s
windows-clang	4m 37s
windows-oldest	6m 37s
windows-static-mt	5m 23s
nightly-build-windows-visual-studio	7m 7s
	59m 49s

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