Docs: Improve WebGLMultisampleRenderTarget page

docs/api/en/renderers/WebGLMultisampleRenderTarget.html

@@ -12,6 +12,7 @@
 
 		<p class="desc">
 			A special render target that can be used to utilize multi-sampled renderbuffers.
+			Heads up: [name] can only be used with a WebGL 2 rendering context.
 		</p>