Track AMP related activity and specs

[iherman]

(This issue was originally raised by @BigBlueHat on the wpub issue list, but moved to this repository as part of the more "general" issues.)

AMP is the progenitor of the Web Packaging spec we are being encouraged to consider for PWP. It is also the source of several other specifications that may be of value to our work, and (consequently) we should be involved in these discussions if possible:
https://github.com/ampproject/amphtml/blob/master/contributing/web-standards-related-to-amp.md#overview-of-web-standards-and-features-related-to-amp