[Issue #38] Update quickstart guide for usability tests

[widal001]

Summary

Updates the quickstart guide for usability tests

• Fixes [Website] Prepare docs for usability tests #38
• Time to review: 5 minutes

Changes proposed

What was added, updated, or removed in this PR.

Updates the quickstart guide:

• Reorganizes the quickstart guide headers
• Adds a "First steps" section that is just a series of commands to get a CommonGrants API up and running
• Adds a more in depth deep dive section with explanations of each command

Context for reviewers

Testing instructions, background context, more in-depth details of the implementation, and anything else you'd like to call out or ask reviewers. Explain how the changes were verified.

Additional information

Screenshots, GIF demos, code examples or output to help show the changes working as expected.