[PATCH]: Clearer documentation when using EVFILT_EXCEPT

[Emil Engler]

Currently it isn't mentioned that a socket is required when using 
EVFILT_EXCEPT with NOTE_OOB. To some experienced users it might be clear 
that it must be a socket but I don't think an additional word would hurt 
anyone.

Index: lib/libc/sys/kqueue.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/kqueue.2,v
retrieving revision 1.42
diff -u -p -u -p -r1.42 kqueue.2
--- lib/libc/sys/kqueue.2       22 Jun 2020 13:42:06 -0000      1.42
+++ lib/libc/sys/kqueue.2       13 Nov 2020 10:46:44 -0000
@@ -315,7 +315,8 @@ Takes a descriptor as the identifier, an
 specified exceptional conditions has occurred on the descriptor.
 Conditions are specified in
 .Fa fflags .
-Currently, a filter can monitor the reception of out-of-band data with
+Currently, a filter can monitor the reception of out-of-band data on a
+socket with
 .Dv NOTE_OOB .
 .It Dv EVFILT_WRITE
 Takes a descriptor as the identifier, and returns whenever