api-string-list.txt: initialize the string_list the easy way

In the demo code blurb, show how to initialize the string_list using
STRING_LIST_INIT_NODUP rather than memset().

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-string-list.txt

@@ -44,10 +44,9 @@ member (you need this if you add things later) and you should set the
 Example:
 
 ----
-struct string_list list;
+struct string_list list = STRING_LIST_INIT_NODUP;
 int i;
 
-memset(&list, 0, sizeof(struct string_list));
 string_list_append(&list, "foo");
 string_list_append(&list, "bar");
 for (i = 0; i < list.nr; i++)