Added README

README.md

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+# Xamarin.Forms Composite Controls
+
+In this repository there are only some tests related to the idea of composite controls and above all have a **Template** property and be able to use **ControlTemplate** to customize a control.
+
+## Let's see more details!
+
+For these tests we have created a Slider Composite control (composed of other Views that make up the control).
+
+![Composite Control](images/composite-control.png)
+
+We have the same visual appearance, properties and events. However, the control has a Template property that allows us to modify the ControlTemplate that defines the control.
+
+We modify the Slider ControlTemplate:
+
+```
+<ControlTemplate x:Key="CustomSliderTemplate">
+    <Grid 
+        VerticalOptions="Center"
+        Margin="10, 0">
+        <BoxView 
+            x:Name="MaximumTrack"
+            BackgroundColor="Green"
+            Margin="6,0"
+            CornerRadius="6"
+            HeightRequest="6"
+            Opacity="0.24"
+            VerticalOptions="Center" />
+        <BoxView 
+            x:Name="MinimumTrack"
+            BackgroundColor="Green"
+            Margin="6,0"
+            CornerRadius="6"
+            HeightRequest="6"
+            HorizontalOptions="Start"
+            InputTransparent="True"
+            VerticalOptions="Center"
+            WidthRequest="0" />
+        <Image        
+            x:Name="Thumb" 
+            Margin="0"
+            BackgroundColor="Transparent"
+            Source="football.png"
+            HeightRequest="36"
+            HorizontalOptions="Start"
+            VerticalOptions="Center"
+            WidthRequest="36" />
+    </Grid>
+</ControlTemplate>
+```
+
+And we use it:
+
+```
+<Slider 
+    ControlTemplate="{StaticResource CustomSliderTemplate}"/>
+```
+
+The result:
+
+![ControlTemplate](images/slider-controltemplate.png)
+
+We can use XAML Hot Reload to adjust the appearance:
+
+![Using XAML Hot Reload](images/xamarinforms-edit-controltemplate.gif)