Added bluepy option to retrieve MAC address, because hcitool won't always work

[ualex73]

I am using a Intel NUC and I noticed that hcitool lescan won't work. On the internet I found out that hcitool is deprecated, so I documented the method using bluepy (the library you are using in your nice project).

[lolouk44]

Thanks a lot for your PR.
I am not keen on asking a user to install anything if it can be avoided, this is kinda the main reason I am using docker for most applications. This is even more true here since the installation is only required for setup.
Instead I will update the readme to use the Xiaomi Mi App, since most users would have installed it anyway...