add a URL to an article about making Apache support PUT

docs/examples/httpput.c

@@ -19,6 +19,9 @@
  * line argument to the URL also given on the command line.
  *
  * This example also uses its own read callback.
+ *
+ * Here's an article on how to setup a PUT handler for Apache:
+ * http://www.apacheweek.com/features/put
  */
 
 size_t read_callback(void *ptr, size_t size, size_t nmemb, void *stream)