Refer to complex binding in howto (#989)

* Refer to complex binding in howto

This patch adds a reference in "How-to" page to point the readers to the
relevant section about how to bind the more complex types. Since "Model
binding" page is not directly referenced from the Readme, many readers
are not aware of it.

This is related to issue #983.

Author: mristin

docs/How-To.md

@@ -180,6 +180,8 @@ The value of fileOption is: null
 
 `System.CommandLine` also knows how to bind other argument types. For example, enums and file system objects such as `FileInfo` and `DirectoryInfo` can be bound. `FileInfo` and `DirectoryInfo` examples of a more general convention whereby any type that has a constructor taking a single `string` parameter can be bound without having to write any custom code. But you can also write your own binding logic for your custom types.
 
+`System.CommandLine` can also parse arbitrary custom types, which is practical for complex applications with long argument lists. See [this section in Model Binding](model-binding.md#more-complex-types) in order to learn more about how to bind the complex types.
+
 ## Middleware Pipeline
 
 While each command has a handler which `System.CommandLine` will route to based on input, there is also a mechanism for short circuiting or altering the input before invoking you application logic. In between parsing and invocation, there is a chain of responsibility, which you can customize. A number of features of `System.CommandLine` make use of this. This is how the `--help` and `--version` options short circuit calls to your handler.
@@ -207,4 +209,3 @@ Hi!
 ```
 
 In the code above, the middleware writes out "Hi!" if the directive "just-say-hi" is found in the parse result. When this happens, because the provided `next` delegate is not called, then the command's normal handler is not invoked.
-