Improve documentation for `Engine.get_idle_frames/get_physics_frames()`

doc/classes/Engine.xml

@@ -37,7 +37,7 @@
 		<method name="get_frames_drawn">
 			<return type="int" />
 			<description>
-				Returns the total number of frames drawn. If the render loop is disabled with [code]--disable-render-loop[/code] via command line, this returns [code]0[/code]. See also [method get_idle_frames].
+				Returns the total number of frames drawn. On headless platforms, or if the render loop is disabled with [code]--disable-render-loop[/code] via command line, [method get_frames_drawn] always returns [code]0[/code]. See [method get_idle_frames].
 			</description>
 		</method>
 		<method name="get_frames_per_second" qualifiers="const">
@@ -49,7 +49,13 @@
 		<method name="get_idle_frames" qualifiers="const">
 			<return type="int" />
 			<description>
-				Returns the total number of frames passed since engine initialization which is advanced on each [b]idle frame[/b], regardless of whether the render loop is enabled. See also [method get_frames_drawn].
+				Returns the total number of frames passed since engine initialization which is advanced on each [b]idle frame[/b], regardless of whether the render loop is enabled. See also [method get_frames_drawn] and [method get_physics_frames].
+				[method get_idle_frames] can be used to run expensive logic less often without relying on a [Timer]:
+				[codeblock]
+				func _process(_delta):
+				    if Engine.get_idle_frames() % 2 == 0:
+				        pass  # Run expensive logic only once every 2 idle (render) frames here.
+				[/codeblock]
 			</description>
 		</method>
 		<method name="get_license_info" qualifiers="const">
@@ -73,7 +79,13 @@
 		<method name="get_physics_frames" qualifiers="const">
 			<return type="int" />
 			<description>
-				Returns the total number of frames passed since engine initialization which is advanced on each [b]physics frame[/b].
+				Returns the total number of frames passed since engine initialization which is advanced on each [b]physics frame[/b]. See also [method get_idle_frames].
+				[method get_physics_frames] can be used to run expensive logic less often without relying on a [Timer]:
+				[codeblock]
+				func _physics_process(_delta):
+				    if Engine.get_physics_frames() % 2 == 0:
+				        pass  # Run expensive logic only once every 2 physics frames here.
+				[/codeblock]
 			</description>
 		</method>
 		<method name="get_physics_interpolation_fraction" qualifiers="const">