Include unix socket in vncviewer usage

We've had support for unix sockets for a while now. Make sure this
is reflected in the -help output and the man page.

Also make some minor tweaks to the section to get everything in
sync with reality.
diff --git a/vncviewer/vncviewer.man b/vncviewer/vncviewer.man
index 729c01d..421290f 100644
--- a/vncviewer/vncviewer.man
+++ b/vncviewer/vncviewer.man
@@ -11,13 +11,17 @@
 .RI [ host ][:: port ]
 .br
 .B vncviewer
+.RI [ options ]
+.RI [ unix\ socket ]
+.br
+.B vncviewer
 .RI [ options ] 
 .B \-listen
 .RI [ port ]
 .br
 .B vncviewer
 .RI [ options ]
-.RI [ .tigervnc file ]
+.RI [ .tigervnc\ file ]
 .SH DESCRIPTION
 .B vncviewer
 is a viewer (client) for Virtual Network Computing.  This manual page documents