Add info about sort in puter.kv.list docs

[reynaldichernando]

the kv list api will return results sorted by the item keys, this isn't documented yet, so we should add it into the kv list docs https://docs.puter.com/KV/list/

also, we need to add an example for it, and linked to playground

for reference on the sort (lexicographically): https://developer.puter.com/tutorials/kv-guide/#sorting

[RaffyLeong]

Hi, I'd like to work on this issue. It would be my first open source contribution. I'll add documentation about sorting with puter.kv.list.

[reynaldichernando]

assigned! @RaffyLeong