Add solutions to functions

solutions/02_functions/functions1.rs

@@ -1 +1,8 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// Some function with the name `call_me` without arguments or a return value.
+fn call_me() {
+    println!("Hello world!");
+}
+
+fn main() {
+    call_me();
+}