from charles "document useful but undocumented property of /proc/.../wait"

Reference: /n/atom/patch/applied2013/wait-length
Date: Sun Jun 16 08:25:52 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/man/3/proc	Sun Jun 16 08:25:32 2013
+++ /sys/man/3/proc	Sun Jun 16 08:25:33 2013
@@ -170,6 +170,10 @@
 a read of
 .B wait
 will block.
+If the file's length is non-zero
+(see
+.IR stat (2)),
+there is at least one wait record to read.
 It is an error for a process to attempt to read its own
 .B wait
 file when it has no children.