Add w3c.json file for W3C tracking purpose

The file provides metadata about the repository so that W3C tools can process
it automatically. See documentation at:
https://w3c.github.io/w3c.json.html

w3c.json

@@ -0,0 +1,5 @@
+{
+  "group": [96877, 125519],
+  "contacts": ["tidoust", "Kangz", "grorg"],
+  "repo-type": ["tests"]
+}