[docs] Add more documentation as well as behaviour

The docs is not clear that data is written to storage only on close. When I ctrl + C a debug instance, the data does not get saved. What if the user uses Task manager to close the app? What if the user's computer shuts down randomly? I suggest the following functionality:

onSet:
- Update data in queue and tell rust what to update
- On rust side, write in a fail safe way. That is
Rename `filename.dat` to `bak/filename.data.bak`
Write to `filename.dat`
- On first load, if `filename.dat` fails, try reading from `bak/filename.data.bak`