Add morphTargetsRelative to documentation

docs/api/en/core/BufferGeometry.html

@@ -144,6 +144,14 @@
 			Hashmap of [page:BufferAttribute]s holding details of the geometry's [page:Geometry.morphTargets morphTargets].
 		</p>
 
+		<h3>[property:Boolean morphTargetsRelative]</h3>
+		<p>
+			Used to control the morph target behavior; when set to true, the morph target data is treated as relative changes to the base geometry,
+			instead of completely replacing the base geometry data.
+
+			Default is *true*.
+		</p>
+
 		<h3>[property:String name]</h3>
 		<p>
 		Optional name for this bufferGeometry instance. Default is an empty string.