Documentation needed for how to fix mismatched entity and/or field definitions

Problem/Motivation

When the Drupal status page reports an error complaining that there are "mismatched entity and/or field definitions" there should be a link to official documentation explaining what caused the error and how to correct it.

Steps to reproduce

I have no idea. I'm looking at the error message, but it doesn't explain what caused it.

Proposed resolution

Create documentation explaining what causes this error and what to do about it.

Remaining tasks

1. Create documentation
2. Link to the documentation from the error message on the status page

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet