message: [rpc]: add example, manual call subscribe ok
diff: @@ -10,6 +10,10 @@ use jsonrpc_pubsub::{typed, SubscriptionId};
  use crate::types::pubsub;
  /// Starcoin PUB-SUB rpc interface.
  +/// Example:
  +/// ```bash
  +/// $ netcat localhost 3030
  +/// {"id":1,"jsonrpc":"2.0","method":"starcoin_subscribe","params":["newPendingTransactions"]}
  #[rpc(server)]
  pub trait StarcoinPubSub {
  /// RPC Metadata
  