Update how_to_use_code_behind.md

Author: elanatframework

doc/how_to_use_code_behind.md

@@ -36,13 +36,9 @@ var builder = WebApplication.CreateBuilder(args);
 
 var app = builder.Build();
 
-+ SetCodeBehind.CodeBehindCompiler.Initialization();
++SetCodeBehind.CodeBehindCompiler.Initialization();
 
-app.Run(async context =>
-{
-+    CodeBehind.CodeBehindExecute execute = new CodeBehind.CodeBehindExecute();
-+    await context.Response.WriteAsync(execute.Run(context));
-});
++app.UseCodeBehind();
 
 app.Run();
 ```