fix: refine csharp example

examples/C#/taosdemo/README.md

@@ -36,7 +36,11 @@ dotnet build -c Release
 ## Usage
 
 ```
-Usage: mono taosdemo.exe [OPTION...]
+Usage with mono:
+$ mono taosdemo.exe [OPTION...]
+
+Usage with dotnet:
+Usage: .\bin\Release\net5.0\taosdemo.exe [OPTION...]
 
         --help                   Show usage.
 

examples/C#/taosdemo/taosdemo.cs

@@ -72,7 +72,7 @@ namespace TDengineDriver
             {
                 if ("--help" == argv[i])
                 {
-                    Console.WriteLine("Usage: mono taosdemo.exe [OPTION...]");
+                    Console.WriteLine("Usage: taosdemo.exe [OPTION...]");
                     Console.WriteLine("");
                     HelpPrint("--help", "Show usage.");
                     Console.WriteLine("");