Add License.txt file, a three clause BSD license.
Add License.txt file, a three clause BSD license.

Kitware/VeloView,Kitware/VeloView,mathstuf/tomviz-superbuild,cjh1/tomviz-superbuild,Kitware/VeloView,OpenChemistry/tomviz-superbuild,Kitware/VeloView,cjh1/tomviz-superbuild,frizaro/Veloview,OpenChemistry/tomviz-superbuild,mathturtle/tomviz-superbuild,Kitware/VeloView,frizaro/Veloview,mathturtle/tomviz-superbuild,frizaro/Veloview,frizaro/Veloview,mathstuf/tomviz-superbuild