Fiy description for FixedUpdate

FixedUpdate is not called in fixed intervals but may be called twice in
a row if framerate is too low.

leitfaden.typ

@@ -118,7 +118,7 @@ When trying this for a collider, it is called _Shape Casting_.
 The game engine loads required assets on startup and then enters the main loop.
 In every frame, the loop will go through several stages (usually this includes `PreUpdate`, `Update`, and `PostUpdate`),
 giving scripts the opportunity to act in these stages.
-There is also a special stage called `FixedUpdate`, that is called with a fixed interval between all invocations, independently of the game's frame rate.
+There is also a special stage called `FixedUpdate`, that is called a fixed number of times per second, independently of the game's frame rate.
 After each iteration of the main loop, the engine will render the world to the screen.
 During rendering, the engine might also perform post-processing steps like antialiasing#footnote[See https://docs.godotengine.org/en/stable/tutorials/3d/3d_antialiasing.html for Godot's options].