adding DOI and arXiv links for NILMTK v0.2 paper
adding DOI and arXiv links for NILMTK v0.2 paper

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