Feedback on cbbackupmgr restore | Couchbase Docs

We need to mention in --map-data that
```
A bucket can be mapped to the bucket, the scope of the same bucket can be mapped to any scope of the same bucket, and the collection of the same scope of the same bucket can only be mapped to any collection of the same scope of the same bucket
```

Otherwise, anyone would face the error below:
> 2023-08-17T11:49:09 ERROR Stdout: b"Error restoring cluster: invalid mapping 'some_map=some_other_map', scopes/collections can only be mapped inside the same bucket\n"