Add missing package readme

Author: kzu

src/PackageReferenceCleaner/PackageReferenceCleaner.csproj

@@ -12,6 +12,10 @@
     <Description>Cleans up PackageReference with PrivateAssets="all" into a one-liner.</Description>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="..\..\readme.md" Link="readme.md" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="NuGetizer" Version="1.0.1" Pack="false" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" Pack="false" />