Missing prompt documentation

[Liupold]

Prompt documentation must be added before the 0.7 release.
The prompt now supports the following :

Operators:
{}, {}-{}, {}:{}: Will download the songs from the list.
{}.p, {}-{}.p, {}:{}.p: Will stream the songs from the list.
{}.l: will show the lyrics

Commands:
.conf : show the config (priority: command line > config file > default)
.ls: show the current song list.
.save {name}: save the current song list.
.lsave: list all the saved song list.
.load {name}: load the saved song list.

Command which may be added:
.cls or .clear: clears the screen
.del {name}: delete a saved song list.
.set {option} {value}: on the fly config update.
.gen: write the current config to config file.
{}.i: show the info of the song.
{}.u: show download url of the song.
{}.t: show the thumbnail url of the song.