Adding license & guidelines for contributing

Author: Amrapali Zaveri

IG-CONTRIBUTING.md

@@ -0,0 +1,17 @@
+Contributions to this repository are intended to become part of Interest Group documents governed by the [Software and Document License](http://www.w3.org/Consortium/Legal/copyright-software). By committing here, you agree to that licensing of your contributions.
+
+If you are not the sole contributor to a contribution (pull request), please identify all contributors in the pull request comment.
+
+To add a contributor (other than yourself, that's automatic), mark them one per line as follows:
+
+```
++@micheldumontier
+```
+
+If you added a contributor by mistake, you can remove them in a comment with:
+
+```
+-@github_username
+```
+
+If you are making a pull request on behalf of someone else but you had no part in designing the feature, you can remove yourself with the above syntax.

WG-LICENSE.md

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+All documents in this Repository are licensed by contributors
+under the 
+[W3C Document License](http://www.w3.org/Consortium/Legal/copyright-documents).
+