added proguard rules

app/proguard.pro

@@ -0,0 +1,8 @@
+# https://github.com/Kotlin/kotlinx.serialization
+-if @kotlinx.serialization.Serializable class **
+-keepclassmembers class <1> { static <1>$Companion Companion; }
+-if @kotlinx.serialization.Serializable class ** { static **$* *; }
+-keepclassmembers class <2>$<3> { kotlinx.serialization.KSerializer serializer(...); }
+-if @kotlinx.serialization.Serializable class ** { public static ** INSTANCE; }
+-keepclassmembers class <1> { public static <1> INSTANCE; kotlinx.serialization.KSerializer serializer(...); }
+-keepattributes RuntimeVisibleAnnotations,AnnotationDefault