added site link to readme

README.md

@@ -2,6 +2,10 @@
 
 Welcome to the Polymer project repo. This is the meta-repo for all things Polymer project - the core team's roadmap, the community code of conduct, and the contributing guide.
 
+## What is Polymer?
+
+Polymer is a web development library based on the Web Components standards, that makes it easy to build composable, interoperable, encapsulated elements. For more information, see the [Polymer project site](https://www.polymer-project.org/1.0/).
+
 ## Table of Contents
 
 * [Roadmap](Roadmap.md): The core project's roadmap - what the core team is looking to work on in the near future.