Add the command line option for specifying a custom config file to the man page.

doc/terminator.1

@@ -55,6 +55,9 @@ Runs \fBthe rest of the command line\fR instead of your default shell or profile
 .B \-\-working\-directory=DIR
 Set the terminal's working directory
 .TP
+.B \-g, \-\-config FILE
+Use the specified FILE for configuration
+.TP
 .B \-r, \-\-role=ROLE
 Set a custom WM_WINDOW_ROLE property on the window
 .TP