This PR updates the contributing documentation to improve the development process for both external contributors and internal DigitalOcean teams.

Changes:

• Added a detailed section on how to test code changes locally.
• Reorganized content with subsections for better readability.
• Adjusted the order of acceptance test commands, moving the full suite section to the bottom to reduce the risk of accidentally running all tests.
• Highlighted that acceptance tests use real resources, emphasizing the potential costs and impact.