message: docs: modify the usage document
diff: @@ -101,11 +101,12 @@ type:
  `bin/ghttp db_name serverPort` or `bin/ghttp serverPort db_name` to start server with serverPort and load database named db_name initially.
  -Attention: the argument db_name and serverPort can be left out
  +(*Attention: the argument db_name and serverPort can be left out*)
  +Attention: the argument serverPort can be left out
  if you leave out the argument serverPort in the commond, then the corresponding value will be set to default as 9000.
  -if you leave out the argument db_name in the commond, then the db_name will set to null which means not to load a database initially.
  +(*if you leave out the argument db_name in the commond, then the db_name will set to null which means not to load a database initially.*)
  URL rules are listed blow:
  