Add request-to-implement and request-to-ship processes

[jschwe]

We should add some documentation (requires discussion, but a concrete proposal could help) on what is expected from potential contributors that want to implement a new feature.

Checklist ideas:

• Will anyone commit to completing / maintaining this implementation long term?
• One person or team effort?

Other considerations:

• Complexity of the feature
• Baseline Widely Available or obscure feature

[jschwe]

I started by taking some of @mrobinson's point from a zulip thread. Feel free to add / edit to the list and / or discuss via comments. Once we agree on a rough shape I guess we could write out some text and open a draft PR.

[nicoburns]

Baseline Widely Available or obscure feature

A couple of other questions:

• "is it a standardised web feature at all" (e.g. Mini Apps have been proposed and are not).
• "has the spec been finalised, or is it still draft“

[jdm]

• Which other browsers ship/intend to ship the feature?