update: readme showing this spec relates to w3

[dchoi27]

Part of branding our repos around w3up

Would still like to rename this repo w3up-specs and other repos like w3protocol to w3up-protocol or w3up

Typed this in Slack, but just so we have it for later, the thought process is:

• All the code we’re writing today (the client, CLI, UI components, etc.) will eventually get wrapped in the NFT.Storage and web3.storage clients / websites. i think we can consider these all “reference implementations” along with the code currently in w3protocol (just a matter of where the code is used)
• The exception is where our code touches specific infra providers. definitely agree that it’d be nice to have the protocol repo be not tied to any infra provider, but i think we’ll naturally be broaching that as we explore implementing this on Saturn, etc. we can also explore things like calling what’s currently w3infra to something like web3.storage-infra or dotStorage-infra