docs: readme tidyup (status, organization, etc.)

[BigLep]

Doing some items I saw while looking fresh at #35

This includes:

1. Moving contribution section up higher since this is important.
2. Updating the status section.
3. Combining about "code structure" both internally and as it relates to other projects.
4. Added a "notable users" section as a call that we'd like to hear from users and fill this in.
5. (bonus - feel free to reject) added some emojis for more color on the page.