Update reference to companion package

Author: AArnott

src/ImmutableObjectGraph.Core.NuGet/ImmutableObjectGraph.Core.NuGet.nuproj

@@ -25,7 +25,7 @@
     <Authors>Andrew Arnott</Authors>
     <Owners>Andrew Arnott</Owners>
     <Summary>Runtime library for immutable types</Summary>
-    <Description>The runtime components behind the parts generated by the ImmutableObjectGraph.T4 package.</Description>
+    <Description>The runtime components behind the types generated with the ImmutableObjectGraph.Generation package.</Description>
     <ReleaseNotes>
     </ReleaseNotes>
     <ProjectUrl>https://github.com/aarnott/immutableobjectgraph</ProjectUrl>
@@ -42,4 +42,4 @@
     <None Include="ImmutableObjectGraph.nuspec" />
   </ItemGroup>
   <Import Project="$(NuProjPath)\NuProj.targets" />
-</Project>
+</Project>