PIMS-383 Create Express API Documentation

[dbarkowsky]

🎯 Summary

PIMS-383

Changes

• Added a README to the /express-api folder that has some ENV information and available commands. This should be expanded upon as more features are included.
• Started a Wiki page here: https://github.com/bcgov/PIMS/wiki/Express-API . There will need to be a link back to the README after it is merged.

🔰 Checklist

• I have read and agree with the following checklist and am following the guidelines in our Code of Conduct document.

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation where required.
• I have tested my changes to the best of my ability.
• My changes generate no new warnings.

[TaylorFries]

well written documentation.