Explain attack, release, delay, threshold (unit, behavior...) in doc

[iver56]

I got an understanding of the params by looking at https://gist.github.com/bastibe/747283c55aad66404046, but it would be nice for future users if it was mentioned in the readme/docs of this repository as well :)

[Fretless14]

I second this! Usually in audio plugins for audio engineers, the threshold is in dBFS, would be great to have that option instead of solely absolute gain.

[pzelasko]

I might find a bit of time soon to add a separate constructor for that.