Use async main in How-To.md examples (#1246)

Author: Meir017

docs/How-To.md

@@ -65,7 +65,7 @@ var parent = new RootCommand("parent")
 The simplest case for invoking your code, if you have a program so simple that it has no inputs beyond invocation itself, would look like this:
 
 ```csharp
-static void Main(string[] args)
+static async Task Main(string[] args)
 {
     var rootCommand = new RootCommand();
 
@@ -74,7 +74,7 @@ static void Main(string[] args)
         /* do something */
     });
 
-    rootCommand.InvokeAsync(args).Wait();
+    await rootCommand.InvokeAsync(args);
 }
 ```
 
@@ -96,7 +96,7 @@ The process of creating these values based on command line input is known as mod
 The most common way that `System.CommandLine` performs model binding is to match option or argument names or aliases to the parameter names on a handler, or to the property names of complex objects passed to a handler. Parameters or properties are matched using a convention that matches camel-cased parameter names to kebab-cased option names. In this example, the option `--an-int` matches parameter `anInt` on the `DoSomething` method.
 
 ```csharp
-static void Main(string[] args)
+static async Task Main(string[] args)
 {
     var rootCommand = new RootCommand();
 
@@ -105,7 +105,7 @@ static void Main(string[] args)
 
     rootCommand.Handler = CommandHandler.Create<int, string>(DoSomething);
 
-    rootCommand.InvokeAsync(args).Wait();
+    await rootCommand.InvokeAsync(args);
 }
 
 public static void DoSomething(int anInt, string aString)