Added a bit of documentation for the WindowManager and its MVVM concept

ReadMe.md

@@ -15,3 +15,118 @@ and it will figure out what the correct view is by name (i.e. `ExampleForm`).
 
 There are unit tests for the whole library, so everything is verifiably
 working on all platforms tested (Linux, Windows, Raspberry).
+
+
+MVVM
+----
+
+MVVM stands for Model-View-ViewModel. It is a way to design GUI applications
+that improves testability and keeps the UI separate from the business logic.
+
+- The Model is the underlying data the application is working with,
+  not designed in any way to facilitate any GUI display or editing
+
+- The ViewModel is like an adapter - it presents the data in the model in
+  a way that can be easily dealt with by the view. For example, sets of
+  items may be exposed as `BindingList<Item>`.
+
+- The View is the UI itself - for example, the main window or a modal dialog
+  that is displayed would be a view, too. Each view has a connected ViewModel
+  and the only code in the view class should be what directly handles the UI,
+  like updating button states when the ViewModel signals a change.
+
+
+Basic Design
+------------
+
+This library implements the MVVM pattern through its `WindowManager` class:
+
+![The WindowManager and its related classes](./Documents/WindowManager.svg)
+
+The `WindowManager` keeps track of all open windows and their view models,
+so your basic `Main()` method, which normally looks like this:
+
+```csharp
+[STAThread]
+static void Main() {
+  Application.EnableVisualStyles();
+  Application.SetCompatibleTextRenderingDefault(false);
+  Application.Run(new MainForm());
+}
+```
+
+Now becomes this:
+
+```csharp
+[STAThread]
+static void Main() {
+  Application.EnableVisualStyles();
+  Application.SetCompatibleTextRenderingDefault(false);
+
+  using(var windowManager = new WindowManager()) {
+    Application.Run(windowManager.OpenRoot<MainViewModel>());
+  }
+}
+```
+
+As you can see, we no longer mention the `MainForm` by name, instead we ask
+the `WindowManager` to construct a new `MainViewModel` and also create a view
+that displays it.
+
+It does so by using a "convention over configuration" approach, meaning it
+assumes that if you request a view for `FlurgleSettingsViewModel`, it will
+look for a view named `FlurgleSettingsView`, `FlurgleSettingsForm`,
+`FlurgeSettingsWindow` or `FlurgleSettingsDialog` class and try to construct
+an instance of that class.
+
+Furthermore, if that class implements the `IView` interface, the view model
+will be assigned to its `DataContext` property, establishing
+the View/ViewModel relationship.
+
+
+Adding an IoC Container
+-----------------------
+
+In the previous example, the view and its view model were constructed using
+`Activator.CreateInstance()` - a method provided by .NET that creates a new
+instance via a type's default constructor.
+
+Most of the time, ViewModels have constructor parameters, however. For example
+to provide the ViewModel with the data it is supposed to be an adapter for.
+You can achieve that by constructing the ViewModel yourself and passing it
+to the `WindowManager.OpenRoot()` or `WindowManager.ShowModal()` methods.
+
+A much better approach is to use a dependency injector - an IoC container with
+automatic constructor parameter injection. My favorite one is Ninject (due to
+its neat setup with a fluent interface), but you can use any container you
+wish, simply by inheriting your own `WindowManager` class:
+
+```csharp
+public class NinjectWindowManager : WindowManager {
+
+  public NinjectWindowManager(IKernel kernel, IAutoBinder autoBinder = null) :
+    base(autoBinder) {
+    this.kernel = kernel;
+  }
+
+  protected override object CreateInstance(Type type) {
+    return this.kernel.Get(type);
+  }
+
+  private IKernel kernel;
+}
+```
+
+Your `NinjectWindowManager` will now use `IKernel.Get()` to construct its
+ViewModels, allowing their constructors to require any services and instances
+you have set up in your Ninject kernel.
+
+```csharp
+class MainViewModel {
+
+  public MainViewModel(IMyService myService, IMySettings mySettings) {
+  	// ...
+  }
+
+}
+```