Add README.md to NuGet package (#1688)

Jint/Jint.csproj

@@ -16,6 +16,10 @@
     <DefineConstants>$(DefineConstants);SUPPORTS_SPAN_PARSE;SUPPORTS_WEAK_TABLE_ADD_OR_UPDATE;SUPPORTS_WEAK_TABLE_CLEAR</DefineConstants>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="../README.md" Pack="true" PackagePath="\"/>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Esprima" />
     <PackageReference Include="Meziantou.Analyzer" PrivateAssets="all" />