Seperate release notes and create quickstart guide

[fitzthum]

This splits the release notes into two files.

First, it creates a quickstart guide, which is an entry point for new users. This is a guide to basic CoCo features. It should be updated with future releases.

Second, it creates a release notes file. This contains information just about this release.

I think it was a bit odd to mix these two things together as one of them pertains just to this release and the other is long lasting. We don't want to have to copy all of the instructions from release to release. Instead we just move them to the quickstart guide and update as necessary.

I also made some tweaks to the documentation that was there. I reworded the use cases a little bit. I think they remain the same, but hopefully it is clearer now. I also added a section that lays out hardware support. I think it is important for new users to be able to understand exactly where the project stands with HW support even if they don't have the hardware. I don't think including this detracts from the ease-of-use.

I also removed some of the limitations that have since been resolved and added a few that weren't on there yet.

There are still a lot of missing pieces. @ryansavino and I will add Kata information soon.

@bpradipt I think we need to shorten the operator installation section significantly, especially since it's at the top of the document.

We are also missing some pieces about running sample encrypted workloads with non-tee. Did we ever end up putting any keys into the rootfs? @stevenhorsman

Also, I changed COCO -> CoCo. I can change this back if it makes people mad. Hopefully these are non-controversial changes given that we still need to add content to the guide.

[c3d]

@fitzthum BTW, the change COCO -> CoCo is one I had to do in our blog draft. I think we need to settle on one spelling once and for all 😄

[fitzthum]

yeah @c3d we will put a link to this on the README and on the main project github page once the release is live.