List new languages supported via multilspy update (Kotlin, Dart)

README.md

@@ -56,6 +56,8 @@ With Serena, we provide
      * Go (untested)
      * C# (untested)
      * Rust (untested)
+     * Kotlin (untested)
+     * Dart (untested)
      
    These languages are supported by the language server library [multilspy](https://github.com/microsoft/multilspy), which Serena uses under the hood.
    But we did not explicitly test whether the support for these languages actually works.