Set notification expiration timeout from 2 milliseconds to -1
Added more detailed instructions about installation

Added an easier and more complete instruction on how and where to install spotify-notify. It will certainly help beginners with the installation. Also it will be faster for "pros" to install the script as they only have to copy-paste a few terminal commands...
Merge pull request #4 from mozzbozz/patch-1

Added more detailed instructions about installation
Merge pull request #3 from PaulVanSchayck/master

Set notification expiration timeout from 2 milliseconds to -1
Merge remote-tracking branch 'upstream/master' into python3
updated readme for python3