[DOC] Add clear steps and/or example for stake pool sunseting #2945
Description
Several validators / stake pool maintainers have had issues trying to wind down their services competely. The only real documentation on the matter is in the README of this repo https://github.com/near/core-contracts/tree/master/staking-pool#owner-only-methods There should be a section in the docs explaining this. Probably also needed to update and complete this: https://near-nodes.io/validator/staking-and-delegation
Can also be done together with #2816