Document signal handling in blacklistd(8).

Reviewed by:	bcr@, 0mp@
Approved by:	re (gjb@)
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D17423

contrib/blacklist/bin/blacklistd.8

@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd June 7, 2016
+.Dd October 5, 2018
 .Dt BLACKLISTD 8
 .Os
 .Sh NAME
@@ -178,7 +178,7 @@ Specify the default rule name for the packet filter rules, usually
 .It Fl r
 Re-read the firewall rules from the internal database, then
 remove and re-add them.
-This helps for packet filters that don't retain state across reboots.
+This helps for packet filters that do not retain state across reboots.
 .It Fl s Ar sockpath
 Add
 .Ar sockpath
@@ -198,6 +198,27 @@ diagnostic messages to
 instead of
 .Xr syslogd 8 .
 .El
+.Sh SIGNAL HANDLING
+.Nm
+deals with the following signals:
+.Bl -tag -width "USR2"
+.It HUP
+Receipt of this signal causes
+.Nm
+to re-read the configuration file.
+.It INT, TERM & QUIT
+These signals tell
+.Nm
+to exit in an orderly fashion.
+.It USR1
+This signal tells
+.Nm
+to increase the internal debugging level by 1.
+.It USR2
+This signal tells
+.Nm
+to decrease the internal debugging level by 1.
+.El
 .Sh FILES
 .Bl -tag -width /usr/libexec/blacklistd-helper -compact
 .It Pa /usr/libexec/blacklistd-helper