docs(managing_deis): add store to backup/restore docs

closes #2104
If you blindly go through all the rest of the settings with `s3cmd` you will land here:
```console
Test access with supplied credentials? [Y/n] 
Please wait, attempting to list all buckets...
ERROR: Test failed: 403 (InvalidAccessKeyId): The AWS Access Key Id you provided does not exist in our records.

Retry configuration? [Y/n] n
```

I assume that's because it's trying to hit Amazon and/or my `.s3cfg` is incomplete. But maybe we should note to ignore the test prompt as it could be confusing.