Add a conformance section.

Closes https://www.w3.org/Bugs/Public/show_bug.cgi?id=22591

Let me know if you think this is sufficient.
The rest of the spec has no new line or indentation after <p>. If you like we can enforce the style automatically using format.py, but last time we discussed that it was blocked on breaking inside attribute values, which I want to do but you do not.