Add VDRplayer to the manual

[rgleason]

VDRplayer has some significant advantages over VDR_pi even though it uses Python and is a script not a plugin.
I think it should be included in the PI Manual.

See OpenCPN/OpenCPN#2470 (comment)
Github https://github.com/transmitterdan/VDRplayer
User Manual https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpn:supplementary_software:nmea_instruments&s[]=vdrplayer#vdrplayer

These are the advantages for VDR filtering.
OpenCPN/OpenCPN#2470 (comment)