docs: Getting Started

[jbmoelker]

Changes

Adds step-by-step instructions for getting started on a new project using Head Start.

Associated issue

Part of #71.

How to test

Review docs/getting-started.md and try out its instructions.

Checklist

• [x] I have performed a self-review of my own code
• [x] I have made sure that my PR is easy to review (not too big, includes comments)
• I have added/updated tests to prove that my feature works (if not possible please explain why)
• [z] I have made changes to the README and if the change affects the project setup (npm commands changed, new service added, environmental variable added)
• I have added a decision log entry if the change affects the architecture or changes a significant technology
• [x] I have notified a reviewer

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