Adding the current volume feature and some changes in readme

[saman]

At the moment script is going to set the volume to the max value, I've tried to add the current volume feature. So, after ads script is going to set the volume on the previous value. Unfortyultly, as Spotify didn't show me any ads, I couldn't test it on my device

Also, I've tried to change some stuff in the readme.

If you think they're okay you can merge it.

[mohaalak]

thanks, wow my readme was wrong in so many levels. but your implementation has a bug sometimes spotify play 2,3 advertimesments consecutively so you script gets the volume that is 1 and set it on currentVol.

[mohaalak]

I merged your commit for readme

[saman]

I've tried to fix it, I'm blind as Spotify is not showing me any ads, I think you've got the idea, it'll be good if you can implement it.