inotify.7: Add missing #include in example program

Reported-by: Jason Etherton <jason@ethertonltd.co.uk>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/inotify.7

@@ -923,6 +923,7 @@ Listening for events stopped.
 #include <stdlib.h>
 #include <sys/inotify.h>
 #include <unistd.h>
+#include <string.h>
 
 /* Read all available inotify events from the file descriptor 'fd'.
    wd is the table of watch descriptors for the directories in argv.