I found some information regarding the Mi Cloud service from Xiaomi China forum (all written in Chinese):
MIUI
To use the service, first we have to log in to the Mi Cloud service. Under the Mi Cloud service, we must turn on the Sync albums:
Phone Desktop -> System folder -> Mi Cloud -> Cloud album -> There are 2 buttons here. Turn on the Sync albums. By default, the Upload via Wi-Fi only is on. We can turn it off, but it will be using our data usage.
And then, we have to store our photos in 2 folders: /SDcard/DCIM/Camera folder or /SDcard/DCIM/Screenshots folder.
Theoretically, once we take a photo, it will automatically sync the photo to the Mi Cloud immediately, but the truth is it really sync but takes hours to sync.
It only can sync photos only, for folders (with photos inside) not yet at the moment.
p/s: sorry for my broken English.