Adding better description to nuspecs

nuget/SkiaSharp.Mac.nuspec

@@ -7,7 +7,7 @@
     <authors>Xamarin Inc.</authors>
     <owners>Xamarin Inc.</owners>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <description>C# bindings for Google's Skia library</description>
+    <description>SkiaSharp is a cross-platform 2D graphics API for .NET platforms based on Google's Skia Graphics Library (https://skia.org/).   It provides a comprehensive 2D API that can be used across mobile, server and desktop models to render images.</description>
     <copyright>Copyright (c) Xamarin Inc. 2016</copyright>
     <licenseUrl>https://github.com/mono/SkiaSharp/blob/master/LICENSE.md</licenseUrl>
     <projectUrl>https://github.com/mono/SkiaSharp</projectUrl>

nuget/SkiaSharp.Windows.nuspec

@@ -7,7 +7,7 @@
     <authors>Xamarin Inc.</authors>
     <owners>Xamarin Inc.</owners>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <description>C# bindings for Google's Skia library</description>
+    <description>SkiaSharp is a cross-platform 2D graphics API for .NET platforms based on Google's Skia Graphics Library (https://skia.org/).   It provides a comprehensive 2D API that can be used across mobile, server and desktop models to render images.</description>
     <copyright>Copyright (c) Xamarin Inc. 2016</copyright>
     <licenseUrl>https://github.com/mono/SkiaSharp/blob/master/LICENSE.md</licenseUrl>
     <projectUrl>https://github.com/mono/SkiaSharp</projectUrl>

nuget/SkiaSharp.nuspec

@@ -7,7 +7,7 @@
     <authors>Xamarin Inc.</authors>
     <owners>Xamarin Inc.</owners>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <description>C# bindings for Google's Skia library</description>
+    <description>SkiaSharp is a cross-platform 2D graphics API for .NET platforms based on Google's Skia Graphics Library (https://skia.org/).   It provides a comprehensive 2D API that can be used across mobile, server and desktop models to render images.</description>
     <copyright>Copyright (c) Xamarin Inc. 2016</copyright>
     <licenseUrl>https://github.com/mono/SkiaSharp/blob/master/LICENSE.md</licenseUrl>
     <projectUrl>https://github.com/mono/SkiaSharp</projectUrl>