Add initial draft of crates policy.

[davidtwco]

I've tried to write up what was discussed and in the notes from the All Hands' organizational meeting. There are a handful of areas that need elaborated on and might not make complete sense as it is but was mentioned in the notes from the meeting. I'd appreciate any further ideas or feedback.

[michaelwoerister]

Thanks for writing up the draft, @davidtwco! ❤️

I added some remarks about questions that I expect to arise.

[davidtwco]

For those following along at home, there's discussion about this draft policy - desired changes and additions - in this Zulip thread.

[davidtwco]

I've rewritten most of the policy based on the review comments and yesterday's steering meeting discussions, would appreciate more feedback.

[nikomatsakis]

Looks great. Left some thoughts. Thanks for doing this @davidtwco

[nikomatsakis]

Looks great. Left some thoughts. Thanks for doing this @davidtwco

[Centril]

Looks great; thanks for the changes :)

[Centril]

Looks great; thanks for the changes :)