Update Pyth documentation

[lgalabru]

• add a Stacks section in Pyth documentation along the other networks that we support. The docs repo is public and you should add a page here:
  https://github.com/pyth-network/documentation/tree/main/pages/documentation/pythnet-price-feeds
• Governance message formats are defined in our governance council ui (xc_admin) here. Would be nice if you add your wire format there.
• We have a tool called contract manager to manage the state of our contracts in various networks. We appreciate if you can add Stacks support there as well. It has two important abstractions: Chain and Contract that you need to implement (here is the source).