feat: add examples with descriptions

exl/02_functions.fzs

@@ -0,0 +1,30 @@
+// If you have some code section which is
+//  duplicated in program several times
+//  then it means your program needs some
+//  functions!
+
+fn doSomeWork()
+{
+  printline("Some work");
+}
+
+// If the function makes some kind of
+//  calculations then you should specify
+//  the result type
+
+fn sum(int a, int b) int
+{
+  return a + b;
+}
+
+// The `return` keyword can be used to
+//  actually return the value from the
+//  function. Also, you can specify list
+//  of arguments that you will use inside
+//  the function
+
+int first = 5;
+int second = 6;
+int result = sum(first, second);
+printline(result);
+