Add XML documentation to NuGet package (#333)

Author: pascalberger

nuspec/nuget/Cake.Issues.Reporting.Generic.nuspec

@@ -30,5 +30,6 @@ See the Project Site for an overview of the whole ecosystem of addins for workin
     <file src="netstandard2.0\System.*.dll" target="lib\netstandard2.0" />
     <!-- Cake ships Roslyn for .NET Core but not for .NET Framework runner -->
     <file src="netstandard2.0\Microsoft.CodeAnalysis*.dll" target="lib\netstandard2.0" />
+    <file src="**\Cake.Issues.Reporting.Generic.xml" target="lib" />
   </files>
 </package>