added link for BIM

utils/exporters/revit/README.md

@@ -1,7 +1,7 @@
 RvtVa3c - Revit Three.js Exporter
 =================================
 
-RvtVa3c is an add-in for [Autodesk Revit](http://en.wikipedia.org/wiki/Autodesk_Revit) that exports the Revit model to a three.js version 4 JSON format.
+RvtVa3c is an add-in for [Autodesk Revit](http://en.wikipedia.org/wiki/Autodesk_Revit) that exports the Revit [BIM](http://en.wikipedia.org/wiki/Building_information_modeling) model to a three.js version 4 JSON format.
 
 RvtVa3c is part of the [vA3C project](https://va3c.github.io), "an open source, browser-based 3D model viewer for AEC models that uses [three.js](https://github.com/mrdoob/three.js) to render 3D geometry in the browser, enabling authors in the AEC industry to easily publish their 3D design work on the web for free.