add ECSY, official examples comments

docs/manual/en/introduction/Libraries-and-Plugins.html

@@ -26,6 +26,11 @@
 
 		<h3>Postprocessing</h3>
 		
+		<p>
+			In addition to the [link:https://github.com/mrdoob/three.js/tree/dev/examples/jsm/postprocessing official three.js postprocessing effects],
+			support for some additional effects and frameworks are available through external libraries.
+		</p>
+
 		<ul>
 			<li>[link:https://github.com/vanruesc/postprocessing postprocessing]</li>
 		</ul>
@@ -38,6 +43,11 @@
 
 		<h3>File Formats</h3>
 
+		<p>
+			In addition to the [link:https://github.com/mrdoob/three.js/tree/dev/examples/jsm/loaders official three.js loaders],
+			support for some additional formats is available through external libraries.
+		</p>
+
 		<ul>
 			<li>[link:https://github.com/gkjohnson/urdf-loaders/tree/master/javascript urdf-loader]</li>
 			<li>[link:https://github.com/NASA-AMMOS/3DTilesRendererJS 3d-tiles-renderer-js]</li>
@@ -68,6 +78,7 @@
 		<ul>
 			<li>[link:https://aframe.io/ A-Frame]</li>
 			<li>[link:https://github.com/pmndrs/react-three-fiber react-three-fiber]</li>
+			<li>[link:https://github.com/ecsyjs/ecsy-three ECSY]</li>
 		</ul>
 
 	</body>