[mb-style] RFC: Add "Keep case" to release packaging list

[Nikki]

Alex Mauer wrote:
> I’d think we should probably divide them into a few RFCs so we don’t end
> up with 30 different RFCs each for one item.

As I said on IRC, I'd rather see them separate. There's no reason why 
they all have to be proposed all in one go right now.

> In particular, I think the following are obvious “Yes”s and could
> probably be RFCed together:
> 
> * Slipcase
> * Box

To me these are not obvious yeses. I have numerous things with boxes or 
slipcases, but they all also have things like jewel cases or cardboard 
sleeves and we don't support multiple packagings yet.

> * Keep case

That is already this proposal and doesn't need to be part of other 
proposals. :P

Nikki