Document -O dw_printf redirect option in manpage

Author: ars-ka0s

Diff for: man/direwolf.1

@@ -155,6 +155,9 @@ x = Silence FX.25 information.
 .BI "-t " "n"
 Text colors.  0=disabled. 1=default.  2,3,4,... alternatives.  Use 9 to test compatibility with your terminal.
 
+.TP
+.BI "-O "
+Redirects all printed output to stderr so stdout can be used as audio device.
 
 .TP
 .B "-p "