Add "Validation" to the RFD template

[alilleybrinker]

During today's QWG, the group agreed it would be good to add a section to the RFD template requiring RFD proposers to specify how any changes they've proposed would be validated.

For example, if a new field is being proposed, what validation would be associated with that field to ensure fields are as correct as possible.

[yousifani16-source]

Fix any problem