Added move developer docs.

Author: grokys

docs/developer/how-viewmodels-are-turned-into-views.md

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+# How ViewModels are Turned into Views
+
+We make use of the  [MVVM pattern](https://msdn.microsoft.com/en-us/library/ff798384.aspx), in which application level code is not aware of the view level. MVVM takes advantage of the fact that `DataTemplate`s can be used to create views from view models.
+
+## DataTemplates
+
+[`DataTemplate`](https://docs.microsoft.com/en-us/dotnet/framework/wpf/data/data-templating-overview)s are a WPF feature that allow you to define the presentation of your data. Consider a simple view model:
+
+```csharp
+public class ViewModel
+{
+  public string Greeting => "Hello World!";
+}
+```
+
+And a window:
+
+```csharp
+public class MainWindow : Window
+{
+  public MainWindow()
+  {
+    DataContext = new ViewModel();
+    InitializeComponent();
+  }
+}
+```
+
+```xml
+<Window x:Class="MyApp.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:local="clr-namespace:MyApp"
+        Content="{Binding}">
+</pfui:DialogWindow>
+
+```
+
+Here we're binding the `Content` of the `Window` to the `Window.DataContext`, which we're setting in the constructor to be an instance of `ViewModel`.
+
+One can choose to display the `ViewModel` instance in any way we want by using a `DataTemplate`:
+
+```xml
+<Window x:Class="MyApp.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:local="clr-namespace:MyApp"
+        Content="{Binding}">
+  <Window.Resources>
+    <DataTemplate DataType="{x:Type local:ViewModel}">
+      
+      <!-- Display ViewModel.Greeting in a red border with rounded corners -->
+	  <Border Background="Red" CornerRadius="8">
+        <TextBlock Binding="{Binding Greeting}"
+      </Border>
+        
+    </DataTemplate>
+  </Window.Resources>
+</pfui:DialogWindow>
+```
+
+This is the basis for converting view models to views.
+
+## ViewLocator
+
+There are currently two top-level controls for our UI:
+
+- [GitHubDialogWindow](../src/GitHub.VisualStudio/Views/Dialog/GitHubDialogWindow.xaml) for the dialog which shows the login, clone, etc views
+- [GitHubPaneView](../src/GitHub.VisualStudio/Views/GitHubPane/GitHubPaneView.xaml) for the GitHub pane
+
+In the resources for each of these top-level controls we define a `DataTemplate` like so:
+
+```xml
+<views:ViewLocator x:Key="viewLocator"/>
+<DataTemplate DataType="{x:Type vm:ViewModelBase}">
+  <ContentControl Content="{Binding Converter={StaticResource viewLocator}}"/>
+</DataTemplate>
+```
+
+The `DataTemplate.DataType` here applies the template to all classes inherited from [`GitHub.ViewModels.ViewModelBase`](../src/GitHub.Exports.Reactive/ViewModels/ViewModelBase.cs) [1]. The template defines a single `ContentControl` whose contents are created by a `ViewLocator`.
+
+The [`ViewLocator`](../src/GitHub.VisualStudio/Views/ViewLocator.cs) class is an `IValueConverter` which then creates an instance of the appropriate view for the view model using MEF.
+
+And thus a view model becomes a view.
+
+[1]: it would be nice to make it apply to all classes that inherit `IViewModel` but unfortunately WPF's `DataTemplate`s don't work with interfaces.

docs/developer/readme.md

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+# Developer Documentation
+
+Documentation for hacking on GitHub for Visual Studio:
+
+- User Interface
+  - [How ViewModels are Turned into Views](how-viewmodels-are-turned-into-views.md)
+  - [Implementing a Dialog View](implementing-a-dialog-view.md)
+  - [Dialog Views with Connections](dialog-views-with-connections.md)
+  - [Multi-Paged Dialogs](multi-paged-dialogs.md)
+