Update WebXRManager.html

docs/api/zh/renderers/webxr/WebXRManager.html

@@ -77,6 +77,11 @@
 		Use this space for visualizing the user's hands when no physical controllers are used.
 		</p>
 
+		<h3>[method:Set getPlanes]()</h3>
+		<p>
+		Returns the set of planes detected by WebXR's plane detection API.
+		</p>
+
 		<h3>[method:String getReferenceSpace]()</h3>
 		<p>
 		Returns the reference space.