Include README.md in NuGet packages

Author: niemyjski

Directory.Build.props

@@ -19,8 +19,13 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <AccelerateBuildsInVisualStudio>true</AccelerateBuildsInVisualStudio>
     <SatelliteResourceLanguages>en</SatelliteResourceLanguages>
+    <PackageReadmeFile>README.md</PackageReadmeFile>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="$(MSBuildThisFileDirectory)README.md" Pack="true" PackagePath="\" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="10.0.201" PrivateAssets="All"/>
     <PackageReference Include="AsyncFixer" Version="2.1.0" PrivateAssets="All" />