Document --list-frames option.

README

@@ -57,6 +57,7 @@ Commands:
  --list-moutputs            | List device monitoring outputs.
  --list-serial              | List device serial ports.
  --list-proc-units          | List device processing units.
+ --list-frames              | List device frame buffers.
 
 Video inputs configuration:
  --vi-name <in_X> <name>    | Set video input port X name.

videohubctrl.1

@@ -89,6 +89,9 @@ input, output ports and monitoring ports.
 \fB\-\-list\-proc-units\fR
 Display device procesing units. Unit numbers, locking status and connected
 video inputs.
+.TP
+\fB\-\-list\-frames\fR
+Display stored frame buffers.
 .SH CONFIGURATION COMMANDS
 .PP
 Everywhere where port needs to be set, you can use the port number or the