Consider additional license/grants for specification text

[bnewbold]

This is basically a follow-on to #218

There have been requests from a few folks (eg, https://bsky.app/profile/torgo.com/post/3l7zy6q7cvn2s) to have more clarity around IP grants for the atproto specification, in particular concerns around patents. The current CC-BY license covers copyright. I haven't heard any requests/concerns raised around trademarks.

An example license that could be used for the specification would be "Community Specification 1.0": https://github.com/CommunitySpecification/Community_Specification/blob/main/1._Community_Specification_License-v1.md

This license seems oriented earound collaborative development of a specification, in a working group. To date, atproto has been primarily developed by the Bluesky team, with feedback and input from the community, but not direct contribution of design or specification text. That means the collaborative aspects of the license don't really apply (eg, the language about existing a working group, or around "contributions"), but this may not really matter. The development process might also become more collaborative in the future, though our plan has been to do any collaborative development within the venue of an independent standards body, not via something like a Bluesky-led RFC process.

Some other options:

• a patent pledge by Bluesky (the company), similar to that described in https://www.protocol.ai/blog/announcing-the-permissive-license-stack/
• re-posting the exiting specification text within an existing standards organization