add readme file

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/trunk@1077 b32b6428-25c9-4566-ad07-03861ab6144f

apps/frontend/polymer/xaal-webcomponents-polymer/README.md

+# README
+
+## Contents
+This directory is related to all xAAL webcomponents developed with Polymer.
+Only Polymer library version v1.0 and higher will be supported. 
+
+## TODO
+[] Add bower package ...