Add missing format fields to m.room.message$m.notice schema.

[jimmycuadra]

The example event shows the format and formatted_body fields like the m.text message type, but these fields do not appear in the schema shown above the example.

[turt2live]

Thanks! Per the contributing guidelines can we get a sign off and changelog entry please?

[jimmycuadra]

Done. It'd be useful to explain the changelog system a little better in the contributing guide. The fact that changelogs/client_server/newsfragments is empty in the repository is confusing. I had to look at another accepted pull request to see if I was doing it right, which adds some friction to contributing. Also, the contributing guide says that only the client-server spec is stable, which is no longer true!

[turt2live]

Normally it does have other fragments in it, but after a release it's fairly empty and boring :(

The contributing guide definitely needs an update though, and not just because it says only the CS API is stable.