Added information that we don't support Python 3
Added information that we don't support Python 3

#387
nilmtk/nilmtk,mmottahedi/nilmtk,AlexRobson/nilmtk,pauldeng/nilmtk,josemao/nilmtk,nilmtk/nilmtk,jaduimstra/nilmtk,HarllanAndrye/nilmtk