message: Fix signAndPost -> signAndBroadcast in README
diff: @@ -158,7 +158,7 @@ async function publishProposal(
  };
  const client = new SigningCosmosClient(apiUrl, authorAddress, signer);
  - return client.signAndPost([msg], fee, memo);
  + return client.signAndBroadcast([msg], fee, memo);
  }
  ```
  