Document the behaviour of the "-o file" option when "file" is a directory

(downloaded file(s) are created inside the directory).

MFC after:	3 days

1 files changed, 4 insertions, 0 deletions

diff --git a/usr.bin/fetch/fetch.1 b/usr.bin/fetch/fetch.1
index 6697f8c58681..f2c7a0b3ea01 100644
--- a/usr.bin/fetch/fetch.1
+++ b/usr.bin/fetch/fetch.1
@@ -144,6 +144,10 @@ A
 argument of
 .Sq Li \&-
 indicates that results are to be directed to the standard output.
+If the
+.Ar file
+argument is a directory, fetched file(s) will be placed within the
+directory, with name(s) selected as in the default behaviour.
 .It Fl P
 .It Fl p
 Use passive FTP.