WIP: Add dotenv

[ltfschoen]

• Add dotenv for private key and use of private endpoint
• Update README to show user how to check if debug_getRawReceipts is supported by a provider using cURL
• Update README with example of how to use Goerli Testnet
• Error if you run command npm run exec-local -- 9438792, where 9438792 is a valid block number, it crashes with error

[-] zkwasm require condition is false
file:///Users/luke/code/github/ltfschoen/zkgraph/api/common/zkwasm_mock.js:79
      throw Error("Abort execution");
            ^

Error: Abort execution

which happens on this line https://github.com/hyperoracle/zkgraph/blob/master/api/exec.js#L81