[skip ci]Add comment for Start in datacoord client (#11200)

Signed-off-by: Nsunby <bingyi.sun@zilliz.com>

internal/distributed/datacoord/client/client.go

@@ -203,6 +203,7 @@ func (c *Client) recall(caller func() (interface{}, error)) (interface{}, error)
 	return ret, err
 }
 
+// Start enables the client
 func (c *Client) Start() error {
 	return nil
 }