Add IPR manager required files

[Yonet]

Before import repository in the IPR manager tool, we need to add the below files:

• [x] Add CONTRIBUTING.md
• [x] Add w3c.json
• [x] Add an index.html that's a bare-bones ReSpec spec ready to be edited.
• [x] Add CODE_OF_CONDUCT.md.

Related immersive-web/administrivia#102