[TD-2598] feature: C# taosdemo, update README.md

tests/examples/C#/taosdemo/README.md

@@ -10,12 +10,14 @@ run C# version taosdemo
 ===
 Usage: mono taosdemo.exe [OPTION...]
 
+        --help            Show usage.
+
         -h                host, The host to connect to TDengine. Default is localhost.
         -p                port, The TCP/IP port number to use for the connection. Default is 0.
         -u                user, The user name to use when connecting to the server. Default is 'root'.
         -P                password, The password to use when connecting to the server. Default is 'taosdata'.
         -d                database, Destination database. Default is 'test'.
-        -a                replica, Set the replica parameters of the database, Default 1, min: 1, max: 3.
+        -a                replica, Set the replica parameters of the database, Default 1, min: 1, max: 5.
         -m                table_prefix, Table prefix name. Default is 't'.
         -s                sql file, The select sql file.
         -M                stable, Use super table.
@@ -26,8 +28,8 @@ Usage: mono taosdemo.exe [OPTION...]
         -l                num_of_cols_per_record, The number of columns per record. Default is 3.
         -T                num_of_threads, The number of threads. Default is 10.
         -r                num_of_records_per_req, The number of records per request. Default is 1000.
-        -t                num_of_tables, The number of tables. Default is 10000.
-        -n                num_of_records_per_table, The number of records per table. Default is 10000.
+        -t                num_of_tables, The number of tables. Default is 1.
+        -n                num_of_records_per_table, The number of records per table. Default is 1.
         -c                config_directory, Configuration directory. Default is '/etc/taos/'.
         -x                flag, Insert only flag.
         -O                order, Insert mode--0: In order, 1: Out of order. Default is in order.