Link to Thread-safe APIs in the Thread class documentation

This closes https://github.com/godotengine/godot-docs/issues/2276.

(cherry picked from commit f50a4b8a3b30ed49757e7a8b180ef6a14ff0260a)

doc/classes/Thread.xml

@@ -7,7 +7,8 @@
 		A unit of execution in a process. Can run methods on [Object]s simultaneously. The use of synchronization via [Mutex] or [Semaphore] is advised if working with shared objects.
 	</description>
 	<tutorials>
-		<link>https://docs.godotengine.org/en/latest/tutorials/threads/using_multiple_threads.html</link>
+		<link title="Using multiple threads">https://docs.godotengine.org/en/latest/tutorials/threads/using_multiple_threads.html</link>
+		<link title="Thread-safe APIs">https://docs.godotengine.org/en/latest/tutorials/threads/thread_safe_apis.html</link>
 	</tutorials>
 	<methods>
 		<method name="get_id" qualifiers="const">