The cloud saves are now available!
The cloud save system is disabled by default. To enable it, go to the main menu setting and ensure that the button with a cloud and Steam icon is not barred.
The process will turn your saved data into a JSON file that you can find here:
WINDOWS: C:\Users\yourname\AppData\LocalLow\Achromi\Master Key
LINUX: $XDG_CONFIG_HOME//unity3d/Achromi/Master Key
MAC: ~/Library/Application Support/Achromi/Master Key
It will then be downloaded through Steam Cloud and replace your previously saved data once you start the game. The JSON is updated when you load the main menu (including after quitting from a loaded save), or quit using the power button on the right.
However, the cloud save system is still in beta. I recommend backing your saves up in case you encounter a bug.
You can find your saves for Master Key in the regedit under HKEY_CURRENT_USER\Software\Achromi\Master Key
Click export to save it as a file anywhere, you can restore this save by double-clicking the exported REG file.
Please report any problem or successful save transfer.