Allow whispering write to specified output

[ahmedsaheed]

Hi @shirayu nice work done here,

I would like to add a feature to whispering.
It would be nice to allow user specify output file where the transcription can be written to like so

whispering --language en --model tiny --output ./index.txt

And in a case where output isn't specified, the default should be done.

Note
I would be very pleased to know your toughts on this issue and also very willing to implement this feature.