Add scaladex badge

This closes #312

Author: ghostbuster91

README.md

@@ -2,12 +2,13 @@
 
 [![Build Status](https://img.shields.io/github/workflow/status/softwaremill/diffx/CI/master)](https://github.com/softwaremill/diffx/actions)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.softwaremill.diffx/diffx-core_2.13/badge.svg)](https://search.maven.org/search?q=g:com.softwaremill.diffx)
+[![diffx-core Scala version support](https://index.scala-lang.org/softwaremill/diffx/diffx-core/latest-by-scala-version.svg)](https://index.scala-lang.org/softwaremill/diffx/diffx-core)
+
+
 [![Gitter](https://badges.gitter.im/softwaremill/diffx.svg)](https://gitter.im/softwaremill/diffx?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 [![Mergify Status](https://img.shields.io/endpoint.svg?url=https://gh.mergify.io/badges/softwaremill/diffx&style=flat)](https://mergify.io)
 [![Scala Steward badge](https://img.shields.io/badge/Scala_Steward-helping-brightgreen.svg?style=flat&logo=data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAA4AAAAQCAMAAAARSr4IAAAAVFBMVEUAAACHjojlOy5NWlrKzcYRKjGFjIbp293YycuLa3pYY2LSqql4f3pCUFTgSjNodYRmcXUsPD/NTTbjRS+2jomhgnzNc223cGvZS0HaSD0XLjbaSjElhIr+AAAAAXRSTlMAQObYZgAAAHlJREFUCNdNyosOwyAIhWHAQS1Vt7a77/3fcxxdmv0xwmckutAR1nkm4ggbyEcg/wWmlGLDAA3oL50xi6fk5ffZ3E2E3QfZDCcCN2YtbEWZt+Drc6u6rlqv7Uk0LdKqqr5rk2UCRXOk0vmQKGfc94nOJyQjouF9H/wCc9gECEYfONoAAAAASUVORK5CYII=)](https://scala-steward.org)
 
-Pretty diffs for case classes.
-
 ## Documentation
 
 diffx documentation is available at [diffx-scala.readthedocs.io](https://diffx-scala.readthedocs.io).