Clarify "You have to set .instanceMatrix.needsUpdate flag to true after called .setMatrixAt()."

docs/api/en/objects/InstancedMesh.html

@@ -80,6 +80,7 @@
 		</p>
 		<p>
 			Sets the given local transformation matrix to the defined instance.
+			You have to set [page:.instanceMatrix][page:BufferAttribute.needsUpdate .needsUpdate] flag to true after called [page:.setMatrixAt]().
 		</p>
 
 		<h2>Source</h2>

docs/api/zh/objects/InstancedMesh.html

@@ -79,6 +79,7 @@
 		</p>
 		<p>
 			设置给定的本地变换矩阵到已定义的实例。
+			调用 [page:.setMatrixAt]() 后，你必须把 [page:.instanceMatrix][page:BufferAttribute.needsUpdate .needsUpdate] 设置为 true。
 		</p>
 
 		<h2>源代码</h2>