Updates specification.md based on #279 proposal

[jawsgrant]

✅ Checklist

• [ X] This pull request has a meaningful title.
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⤴️ Summary

Per proposal in #279 updates specification.md
Restructuring
Adds roles section

🌂 Related issues

Relates to #279

🙋 Acknowledging contributors

• [ X] All contributors to this pull request are already named in the table of contributors in the README file.
• The following people should be added to the table of contributors in the README file:

[craddm]

I agree with this restructuring, and think adding brief descriptions of the roles at the end makes sense.

Comments above are to fix linting errors.