Document the "sig" function parameter.

Submitted by:	James Raynard

lib/libc/gen/signal.3

@@ -127,6 +127,9 @@ is possible on a descriptor (see
 .El
 .Pp
 The
+.Fa sig
+parameter specifies which signal was received.
+The
 .Fa func
 procedure allows a user to choose the action upon receipt of a signal.
 To set the default action of the signal to occur as listed above,

lib/libc/sys/sigaction.2

@@ -117,7 +117,8 @@ the signal to be delivered, and
 the signal mask associated with the handler to be invoked.
 .Pp
 .Fn Sigaction
-assigns an action for a specific signal.
+assigns an action for a signal specified by
+.Fa sig .
 If
 .Fa act
 is non-zero, it