Add warning to readme about bad license about sso

[SumianVoice]

Ironically, due to the wording of fair use: "substantial", you're probably in less legal trouble just sampling some random all rights reserved music and extracting instrument samples from that, than you are from using samples from a "free" sample pack. It could be argued I suppose, that using 50 SSO samples (5%) is not substantial, but it's much more substantial than 3s of a 1h piece.

[SumianVoice]

Also found a similar alternative, with some of the samples even being of higher quality:
University of Iowa Electronic Music Studios - Musical Instrument Samples
They are not cropped or modified, just raw .aiff files, so they need editing to be useful in music production.

[peastman]

I'm closing this as a duplicate of #4. As noted there, the license only applies to the sfz files, not the samples. As for the samples, you'll have to decide for yourself whether you're ok with the due diligence Mattias did when selecting them (as described in the README). Note that the University of Iowa collection is one of the sources he took his samples from.