Add AOM Headers

[cconcolato]

Other specifications from the Storage and Transport Format WG have a common header, see:

• https://aomediacodec.github.io/av1-hdr10plus/
• https://aomediacodec.github.io/av1-isobmff/
• https://aomediacodec.github.io/av1-avif/

The header includes:

• the status as an AOM document: WD, WGA, FD
• various links
• editors

This can be done by adopting Bikeshed or Respec as editing framework.

[cconcolato]

This would also allow generating the conformance section automatically as in https://aomediacodec.github.io/av1-avif/#conformance instead of https://aomediacodec.github.io/av1-mpeg2-ts/#modal-verbs-terminology