Update Docs: Testnet Release How-To, Upgrade Proposal Steps, and cosmovisor Docs

[jdfigure]

Upgrade the (README.md)[https://github.com/provenance-io/testnet/blob/main/README.md] to include MVP instructions related to testnet upgrade proposal process:

• Document usage of cosmovisor and how a Node (including local dev) sets up cosmovisor
• Document sample upgrade proposal via CLI
• Document sample governance vote