Spark intro scp command is incomplete

The spark intro contains the following invalid command:
```
local_machine:~$ scp -r -i   ubuntu@:~/price_data
```
It should actually be something like:
```scp -r -i <PATH_TO_SSH_KEY_FILE> <PATH_TO_PRICE_DATA_FOLDER> ubuntu@<DNS_FOR_MASTER_NODE>:~/price_data```