Created OTPFactory overview (markdown)

OTPFactory-overview.md

@@ -0,0 +1,61 @@
+In case you are working on an authenticator app, you can use `OTPFactory` to handle code re-generation and timer updates
+## Configure factory
+To configure factory just simply pass an `OTPConfiguration` object to constructor:
+```csharp
+OTPFactory factory = new (config);
+```
+You can update configuration any time by updating `Configuration` property
+
+## Subscribe to events
+To keep code up to date on the UI side, subscribe to `CodeUpdated` event:
+```csharp
+factory.CodeUpdated += (newCode) =>
+{
+    // Update your data here
+    this.codeLabel.Text = newCode.GetCode();
+};
+```
+Also it could be useful to subscribe to `PropertyChanged` event, since it occurs every second to keep code countdown up to date (countdown update frequency is set on instance constructor by parameter `timeUpdateInterval` in milliseconds)
+```csharp
+OTPFactory factory = new (config);    // use 'new (config, 100)' to update countdown every 100 milliseconds
+factory.PropertyChanged += (s, e) =>
+{
+    if (e.PropertyName == nameof(factory.TimeLeft))
+        this.countdownLabel.Text = factory.TimeLeft.ToString();
+};
+```
+
+## Use MVVM pattern with OTPFactory
+`OTPFactory` object is MVVM ready, so you can use it as is in your ViewModel
+```csharp
+public class MyViewModel : ViewModelBase
+{
+    private OTPFactory _factory = new (OTPConfiguration.GenerateConfiguration("FoxDev Studio", "eugene@xfox111.net"));    // Example value
+    public OTPFactory Factory
+    {
+        get => _factory;
+        set => SetProperty(ref _factory, value);
+    }
+}
+```
+```xaml
+<ContentPage
+    ...
+    xmlns:vm="Your.ViewModel.Namespace">
+    
+    <ContentPage.BindingContext>
+        <vm:MyViewModel/>
+    </ContentPage.BindingContext>
+
+    <StackLayout>
+        <Label Text="{Binding Factory.Configuration.Issuer}" FontSize="28"/>
+        <Label Text="{Binding Factory.Configuration.AccountName}" FontAttributes="Italic"/>
+        <Label Text="{Binding Factory.CurrentCode.Code}"/>
+        <Label Text="{Binding Factory.TimeLeft}"/>
+    </StackLayout>
+    ...
+</ContentPage>
+```
+
+## Dispose OTPFactory
+When you don't need `OTPFactory` anymore it is important to dispose it to prevent memory leaks. To do so just simply call `OTPFactory.Dispose()` or use it with `using keyword`