Write a Next Steps with Kit doc

[bmicklea]

Describe the problem you're trying to solve
The new Quick Start does a good job of getting someone familiar with the basic Kit commands, but it doesn't go into Kitfile authorship or other critical commands.

Describe the solution you'd like
A Next Steps with Kit doc that follows from the Quick Start would help new users to build their own ModelKits and learn how to take advantage of tagging and registry managment.