docs: using publishBrandInfo to make ERTP brands available in vstorage

[0xpatrickdev]

If a contract developer create a brand/issuer in their contract, they need a way to share the resulting boardId with an off chain client if the client wishes to make an offer using the brand.

One way to do this is by using the publishBrandInfo helper:

• https://github.com/Agoric/agoric-sdk/blob/d6f50e32f6f19bb14cfe4530812609dff00d21b8/packages/smart-wallet/test/start-game1-proposal.js#L28-L36
• https://github.com/Agoric/agoric-sdk/blob/d6f50e32f6f19bb14cfe4530812609dff00d21b8/packages/smart-wallet/test/addAsset.test.js#L327-L373

The docs section should show the developer how to publish from the contract side and how to read from the dapp/offchain client side.

[0xpatrickdev]

Question - is it a requirement to produce the issuer in the core-eval? Or this is only needed if the proposer wants to make the issuer available in the bootstrap space for future proposals? cc @dckc

https://github.com/Agoric/agoric-sdk/blob/d6f50e32f6f19bb14cfe4530812609dff00d21b8/packages/smart-wallet/test/start-game1-proposal.js#L51-L53