[DOCS] Minor classref updates.

doc/classes/SceneTreeTimer.xml

@@ -1,8 +1,17 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="SceneTreeTimer" inherits="Reference" category="Core" version="3.1">
 	<brief_description>
+		One-shot timer.
 	</brief_description>
 	<description>
+		A one-shot timer managed by the scene tree, which emits [signal timeout] on completion. See also [method SceneTree.create_timer].
+		As opposed to a [class Timer], does not require the instantiation of a node. Commonly used to create a one-shot delay timer as in the following example:
+		[codeblock]
+		func some_function():
+			print("start")
+			yield(get_tree().create_timer(1.0), "timeout")
+			print("end")
+		[/codeblock]
 	</description>
 	<tutorials>
 	</tutorials>
@@ -12,11 +21,13 @@
 	</methods>
 	<members>
 		<member name="time_left" type="float" setter="set_time_left" getter="get_time_left">
+			The time remaining.
 		</member>
 	</members>
 	<signals>
 		<signal name="timeout">
 			<description>
+				Emitted when the timer reaches 0.
 			</description>
 		</signal>
 	</signals>