add --subs-name requirement in README.md

Author: zzzming

README.md

@@ -13,9 +13,11 @@ GET `admin/v2/functions/connectors` displays the nar is loaded successfully as
 
 `EFFECTIVELY_ONCE` processing guarantees is required since it implements message [cumulative acknowledgement](https://github.com/apache/pulsar/blob/master/pulsar-functions/instance/src/main/java/org/apache/pulsar/functions/source/PulsarSource.java#L129)
 
+Option `--subs-name` is required too.
+
 Create a sink by uploading a nar file.
 ```
-$ bin/pulsar-admin sinks create --archive ./connectors/pulsar-io-s3-1.0.nar --inputs aws-s3-input-topic --name aws-s3-test --sink-config-file ./connectors/pulsar-s3-io.yaml --processing-guarantees EFFECTIVELY_ONCE --subs-position Earliest --sub-name auniquename
+$ bin/pulsar-admin sinks create --archive ./connectors/pulsar-io-s3-1.0.nar --inputs aws-s3-input-topic --name aws-s3-test --sink-config-file ./connectors/pulsar-s3-io.yaml --processing-guarantees EFFECTIVELY_ONCE --subs-position Earliest --subs-name auniquename
 "Created successfully"
 ```