dead link in readme: gather-based warping ref

[Christoph Haag]

gather-based warping ref: http://www.cs.virginia.edu/~gfx/pmwiki/index.php?n=Pubs.Yang2011IBB

Not Found
The requested URL /~gfx/pmwiki/index.php was not found on this server.

[Yana/Yannic Haupenthal]

maybe you could link to the archive?

[Florian Ziesche]

Thanks, I replaced it with a link to a copy from one of the other authors + added the archive link in case this may be useful.