Merge pull request #20620 from gonnavis/DocsInstancedMesh.setMatrixAt

Docs: Clarify InstancedMesh.setMatrixAt() needs update.

docs/api/en/objects/InstancedMesh.html

@@ -80,6 +80,7 @@
 		</p>
 		<p>
 			Sets the given local transformation matrix to the defined instance.
+			Make sure you set [page:.instanceMatrix][page:BufferAttribute.needsUpdate .needsUpdate] to true after updating all the matrices.
 		</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。
+			请确保在更新所有矩阵后将 [page:.instanceMatrix][page:BufferAttribute.needsUpdate .needsUpdate] 设置为true。
 		</p>
 
 		<h2>源代码</h2>