Create README.md

Author: usercode

README.md

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+# WPF.ImageEffects
+GPU-based image effects (brightness, contrast) for WPF
+
+https://www.nuget.org/packages/WPF.ImageEffects
+
+[![nuget](https://img.shields.io/nuget/v/WPF.ImageEffects.svg)](https://www.nuget.org/packages/WPF.ImageEffects)
+
+## How to use it ##
+
+1. Add namespace ("http://usercode.de/wpf.imageeffects") to root node:
+
+```XAML
+<Window x:Class="WPF.ImageEffects.Demo.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:imageeffects="http://usercode.de/wpf.imageeffects"
+        xmlns:local="clr-namespace:WPF.ImageEffects.Demo"
+        Title="MainWindow">
+```
+
+2. Place shader effect to image control
+
+```XAML
+<Slider x:Name="sliderBrightness" Minimum="-1" Maximum="1" Value="0" />
+<Slider x:Name="sliderContrast" Minimum="-1" Maximum="1" Value="0" />
+
+<Image x:Name="image">
+            <Image.Effect>
+                <imageeffects:BrightnessContrastEffect 
+                                        Brightness="{Binding Value, ElementName=sliderBrightness}" 
+                                        Contrast="{Binding Value, ElementName=sliderContrast}" />
+            </Image.Effect>
+</Image>
+```