message: docs(README): instruction to find RPC port
diff: @@ -67,6 +67,8 @@ target/release/nervos
  ### Send Transaction via RPC
  +Find RPC port in the log output, the following command assumes 3030 is used:
  +
  ```shell
  curl -d '{"id": 2, "jsonrpc": "2.0", "method":"send_transaction","params": [{"version":2, "inputs":[], "outputs":[], "groupings":[]}]}' \
  -H 'content-type:application/json' 'http://localhost:3030'
  