Add release notes.

Author: AArnott

DiffPlex.NuGet/DiffPlex.NuGet.nuproj

@@ -37,8 +37,7 @@
     <Summary>
     </Summary>
     <Description>DiffPlex is a diffing library that allows you to programatically create text diffs. DiffPlex is a fast and tested library which is used by CodePlex to provide its source code diffing functionality.</Description>
-    <ReleaseNotes>
-    </ReleaseNotes>
+    <ReleaseNotes>Now a PCL (portable library) that targets .NET 4.0, Silverlight 5.0, Windows 8.0, Windows Phone 8.0, Windows Phone Appx 8.1.</ReleaseNotes>
     <ProjectUrl>http://diffplex.codeplex.com/</ProjectUrl>
     <LicenseUrl>http://diffplex.codeplex.com/license</LicenseUrl>
     <Copyright>