adding appliance_metadata and referencing docs/standard_names/appliances.txt
adding appliance_metadata and referencing docs/standard_names/appliances.txt

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