Added documentation for scene updater functions (ManimCommunity#2663)

* added scene updater documentation

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: behackl

manim/scene/scene.py

@@ -345,7 +345,22 @@ def update_meshes(self, dt):
             for mesh in obj.get_family():
                 mesh.update(dt)
 
-    def update_self(self, dt):
+    def update_self(self, dt: float):
+        """Run all scene updater functions.
+
+        Among all types of update functions (mobject updaters, mesh updaters,
+        scene updaters), scene update functions are called last.
+
+        Parameters
+        ----------
+        dt
+            Scene time since last update.
+
+        See Also
+        --------
+        :meth:`.Scene.add_updater`
+        :meth:`.Scene.remove_updater`
+        """
         for func in self.updaters:
             func(dt)
 
@@ -503,10 +518,50 @@ def remove(self, *mobjects):
                 self.restructure_mobjects(mobjects, list_name, False)
             return self
 
-    def add_updater(self, func):
+    def add_updater(self, func: Callable[[float], None]) -> None:
+        """Add an update function to the scene.
+
+        The scene updater functions are run every frame,
+        and they are the last type of updaters to run.
+
+        .. WARNING::
+
+            When using the Cairo renderer, scene updaters that
+            modify mobjects are not detected in the same way
+            that mobject updaters are. To be more concrete,
+            a mobject only modified via a scene updater will
+            not necessarily be added to the list of *moving
+            mobjects* and thus might not be updated every frame.
+
+            TL;DR: Use mobject updaters to update mobjects.
+
+        Parameters
+        ----------
+        func
+            The updater function. It takes a float, which is the
+            time difference since the last update (usually equal
+            to the frame rate).
+
+        See also
+        --------
+        :meth:`.Scene.remove_updater`
+        :meth:`.Scene.update_self`
+        """
         self.updaters.append(func)
 
-    def remove_updater(self, func):
+    def remove_updater(self, func: Callable[[float], None]) -> None:
+        """Remove an update function from the scene.
+
+        Parameters
+        ----------
+        func
+            The updater function to be removed.
+
+        See also
+        --------
+        :meth:`.Scene.add_updater`
+        :meth:`.Scene.update_self`
+        """
         self.updaters = [f for f in self.updaters if f is not func]
 
     def restructure_mobjects(