Add a simple explanation and license
VerbNet 1.0 - 2003-02-21

ftp://ftp.cis.upenn.edu/pub/kipper/Verbnet-02.21.03.tar.gz
http://web.archive.org/web/20051109115814/http://www.cis.upenn.edu/~bsnyder3/verbnet/download/Verbnet-02.21.03.tar.gz
Verbnet 1.5 - 2004-06-21

ftp://ftp.cis.upenn.edu/pub/kipper/verbnet-20040621.tar.gz
VerbNet 2.0 - 2004-12-03

ftp://ftp.cis.upenn.edu/pub/kipper/verbnet-20041203.tar.gz
VerbNet 2.x (2.1?) - 2005-07-06

ftp://ftp.cis.upenn.edu/pub/kipper/verbnet-20050706.tar.gz
VerbNet 2.x (2.2?) - 2005-12-06

ftp://ftp.cis.upenn.edu/pub/kipper/verbnet-20051206.tar.gz
VerbNet 2.3 - unknown date

https://bitbucket.org/gchrupala/delta-h/src/4edcbd7e810f/ext_sem_features/verbnet-2.3/?at=default
VerbNet 3.1 - 2012-07-24

http://verbs.colorado.edu/verb-index/vn/verbnet-3.1.tar.gz
VerbNet 3.2 - 2013-04-26

http://verbs.colorado.edu/verb-index/vn/verbnet-3.2.tar.gz