Add the README to the NuGet package

See https://devblogs.microsoft.com/nuget/add-a-readme-to-your-nuget-package/

Author: 0xced

src/Serilog.Settings.Configuration/Serilog.Settings.Configuration.csproj

@@ -12,6 +12,7 @@
     <AssemblyName>Serilog.Settings.Configuration</AssemblyName>
     <PackageTags>serilog;json</PackageTags>
     <PackageIcon>icon.png</PackageIcon>
+    <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
     <PackageProjectUrl>https://github.com/serilog/serilog-settings-configuration</PackageProjectUrl>
     <PackageReleaseNotes>$(PackageProjectUrl)/releases</PackageReleaseNotes>
@@ -31,6 +32,7 @@
     <PackageReference Include="PolySharp" Version="1.13.1" PrivateAssets="All" />
     <PackageReference Include="Serilog" Version="2.12.0" />
     <None Include="..\..\assets\icon.png" Pack="true" PackagePath="" Visible="false" />
+    <None Include="..\..\README.md" Pack="true" PackagePath="" />
   </ItemGroup>
 
   <ItemGroup>