Added link to the Shannon reference implementation

[sashahilton00]

Stumbled across the Qualcomm Shannon Cipher reference implementation whilst rewriting the authentication part of librespot, added a link to a copy of it in my repo.

[plietar]

What's the original source for this ? I'd rather point to that instead

[sashahilton00]

So would I, but it was pulled from web.archive.org, which isn't the greatest place to rely on for long term hosting... https://web.archive.org/web/20081010141647/http://www.qualcomm.com.au/PublicationsDocs/Shannon-1.0.tgz the original url is http://www.qualcomm.com.au/PublicationsDocs/Shannon-1.0.tgz though it's long gone.