l1-s8 add common code sample

Author: Alex009

mpp-library/src/commonMain/kotlin/HelloWorld.kt

@@ -0,0 +1,9 @@
+/*
+ * Copyright 2019 IceRock MAG Inc. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+object HelloWorld {
+    fun print() {
+        println("hello common world")
+    }
+}