Warning about SAKs in release notes

Witness the following:

f (x :: a) = x

type T (x :: a) = x

In f, a is considered inferred. In T, a is considered specified. This is silly. Though it hasn't yet been concretely described, we want to leave the door open to changing the way this works in types, whenever -XStandaloneKindSignatures is enabled. I thought that putting a warning in a release note would be helpful.

It it's too late / not a good idea, I can live without this.