Added licence for NUnit
Added licence for NUnit

malcolmr/nodatime,nodatime/nodatime,malcolmr/nodatime,zaccharles/nodatime,nodatime/nodatime,malcolmr/nodatime,zaccharles/nodatime,jskeet/nodatime,jskeet/nodatime,malcolmr/nodatime,zaccharles/nodatime,BenJenkinson/nodatime,BenJenkinson/nodatime,zaccharles/nodatime,zaccharles/nodatime,zaccharles/nodatime