Document the policy of not using /TR templates on github.io

[plehegar]

We don't allow the use the /TR templates on github.io

We only authorize editor's draft and CG reports on github.io.

We tolerate the corner case of using github.io to prepare an upcoming publication but certainly not as a replacement to the editor's draft.

[svgeesus]

Agreed (and the third point needs careful wording).