Merge GeoffreyBooth proposal into README

[GeoffreyBooth]

@rattrayalex I wanted to submit this as a PR rather than just overwriting the README, since I changed or removed some of the text you had written in the README. Please merge in if my edits look good to you.

[mrmowgli]

Looks great to me, seems to have everything in there! +1

[rattrayalex]

Thanks @GeoffreyBooth ! I like what I see.

It seems a bit long for a README. Thoughts on how we could shorten it? Would you like me to try to help edit it down? Also happy to merge as-is if you think that's best.

[GeoffreyBooth]

Why don’t we merge it and then we can discuss what to cut or split out into separate files. On the one hand I feel like the proposal could be its own file, but on the other I feel like that’s the central thing in this repo that we want people to notice and comment on, so it should pop up on the first page. I dunno.

One thing we should maybe create as a separate top-level markdown file is a list of what we’ve agreed on. For example it seems like we’ve reached a consensus on const, so it would be good to put the plan in writing so it’s clearer than a stream of issue comments. Maybe the “way forward” section could become part of that file, and that’s a living document where we hash out the specifics of how we’re going to achieve our goals.

[rattrayalex]

I wanted to submit this as a PR rather than just overwriting the README

We should probably always send as PR for anything other than a typo fix, for transparency.

[rattrayalex]

I'd rather not to a sloppy merge into the README; if we like this as it is, cool, but if we think we can do better I'd rather that happen before merging.

[GeoffreyBooth]

How about the “A New Compiler” and ”Relevant Discussions” sections get split into their own files? “A New Compiler” is very specific about the technical plan, which doesn’t need to be in a top-level README; and “Relevant Discussions” is becoming less relevant now that the coffeescript6 repo itself exists, and our discussions (in my opinion) supersede any older ones from the coffeescript main repo.

[rattrayalex]

Nice, that sounds good to me!

[rattrayalex]

Nice, thanks! Probably can also move the "possible alternatives" to reference file as well. I can do in a follow-on if you prefer.