Update how environment variables are set up in Que Pasa installation

This description of how to set up the env variables to run Que Pasa is confusing because they create a .env file but don't actually add anything to it. This MR:

• Changes from using a new .env file to updating the default env file to avoid confusion between the files
• Has the user update the values in that file and then source it
• Removes the screencap of a terminal window and commands that don't work
• Updates the RPC node. Que Pasa fails with the Marigold RPC because that's a snapshot node and for some reason when a client requests a block that it doesn't have, it gets the data from a full node but also returns a 404, which causes que pasa to throw an error. You can verify that by running curl -v https://mainnet.tezos.marigold.dev/chains/main/blocks/2. -- Edit: A fix is in flight for this issue.