Tweaks to the configuration explanation

[TeresiaOlsson]

I have made some suggestions for the configuration explanation. Most important ones:

• I removed the grid because it made it difficult to see both versions at the same time without having to scroll to the side.
• Removed that unknown fields will be rejected because that might not always be the case. It depends if you choose to validate or not which is planned to be made optional so you can skip validating every time the config is loaded if you want to save some loading overhead.
• Removed the section about how to find the fields. I liked that section a lot but thought it would be more useful in the how-to guide for how to create the configuration so plan to move it there.
• Remove the configuration item section since it had become obsolete.