Documented that mutexes are implemented recursively

(cherry picked from commit 46bbeb2b601787c3f2a1deb358c3a56e9198f5a2)

doc/classes/Mutex.xml

@@ -14,18 +14,21 @@
 			<return type="void" />
 			<description>
 				Locks this [Mutex], blocks until it is unlocked by the current owner.
+				[b]Note:[/b] This function returns without blocking if the thread already has ownership of the mutex.
 			</description>
 		</method>
 		<method name="try_lock">
 			<return type="int" enum="Error" />
 			<description>
 				Tries locking this [Mutex], but does not block. Returns [constant OK] on success, [constant ERR_BUSY] otherwise.
+				[b]Note:[/b] This function returns [constant OK] if the thread already has ownership of the mutex.
 			</description>
 		</method>
 		<method name="unlock">
 			<return type="void" />
 			<description>
 				Unlocks this [Mutex], leaving it to other threads.
+				[b]Note:[/b] If a thread called [method lock] or [method try_lock] multiple times while already having ownership of the mutex, it must also call [method unlock] the same number of times in order to unlock it correctly.
 			</description>
 		</method>
 	</methods>