Add example of a definition of a Set field in a Collection field to Set/Collection Docs

[nestordedios]

There is an example how to define and print Set field in a collection here https://docs.boltcms.io/5.0/howto/transform-repeaters-to-sets-and-collections#repeater-collection-with-1-set.

I think it would be helpful to add that example on the Collection and Set fields docs as well?

[I-Valchev]

Yes, certainly!