endian: add documentation on endian typedefs.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/endian/_info

@@ -15,6 +15,8 @@
  * order (almost everyone else).
  *
  * This module provides conversion routines, inspired by the linux kernel.
+ * It also provides leint32_t, beint32_t etc typedefs, which are annotated for
+ * the sparse checker.
  *
  * Example:
  *	#include <stdio.h>