System.Text.Json workaround in .netCore 3

Author: xfischer

README.md

@@ -28,6 +28,14 @@ Point point = JsonConvert.DeserializeObject<Point>(json);
 
 See the [Tests](https://github.com/GeoJSON-Net/GeoJSON.Net/tree/master/src/GeoJSON.Net.Tests) for more examples.
 
+## Special considerations for ASP.Net Core 3+
+
+System.Text.Json is the default (recommended) serializer. GeoJSON.Net **does not play well with System.Text.Json**. Here are the recommended steps as a workaround:
+
+- add the "Microsoft.AspNetCore.Mvc.NewtonsoftJson" NuGet Package
+- add "services.AddControllers().AddNewtonsoftJson();" to your service configuration.
+
+(Thanks for @jrowe88 for pointing this out)
 
 ## Contributing
 Highly welcome! Just fork away and send a pull request. We try and review most pull requests within a couple of days. There is now a version 2.0.0 branch. I've created this ready for any breaking changes and any extra features and would encourage anything that isn't a bug fix to go in there.