updated docs for convert to add an example for value class conversion

Author: Jolanrensen

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/samples/api/Modify.kt

@@ -216,6 +216,18 @@ class Modify : TestBase() {
         // SampleEnd
     }
 
+    @JvmInline
+    value class IntClass(val value: Int)
+
+    @Test
+    @TransformDataFrameExpressions
+    fun convertToValueClass() {
+        // SampleStart
+        dataFrameOf("value")("1", "2")
+            .convert("value").to<IntClass>()
+        // SampleEnd
+    }
+
     @Test
     @TransformDataFrameExpressions
     fun convertAsFrame() {