Flesh out Validation Errors Documentation

[robons]

Assuming we know how frequently our internal team has experienced the different validation errors (as set up in #254) from our own use of the prototype, we should focus on the top 5-10 errors and improve the documentation selectively there to make it even easier to understand how to fix the thing.

Provide more practical examples of the different specific types of this validation error it's possible to see and explain why the constraint enforced by the error is necessary.