Please add homebridge-xiaomi-airpurifier-km81

[Albert711]

https://www.npmjs.com/package/homebridge-xiaomi-airpurifier-km81
Thank you in advance!

[nxhack]

@Albert711

Please test it.
https://github.com/nxhack/openwrt-node-packages/tree/master/node-homebridge-xiaomi-airpurifier-km81