Update docker_remote_api_v1.14.md

It is a tar stream, you should mention that somehow.

Here is the proof:

```
	host:~$ docker run -t -i ubuntu:14.04 bash
	root@c39be4c7b7c8:/# echo "my file contents" > abc
	root@c39be4c7b7c8:/# cat abc
	my file contents
	root@c39be4c7b7c8:/# exit
	host:~$ curl -H "Content-Type: application/json" -d '{"Resource":"/abc"}' http://localhost:4500/containers/c39be4c7b7c8/copy 
	abc0100644000000000000000000000002112402102531007674 0ustar0000000000000000my file contents
	host:~$ curl -H "Content-Type: application/json" -d '{"Resource":"/abc"}' http://localhost:4500/containers/c39be4c7b7c8/copy > response_content
	  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
	                                 Dload  Upload   Total   Spent    Left  Speed
	100  2067  100  2048  100    19  56968    528 --:--:-- --:--:-- --:--:-- 58514
	host:~$ tar xvf response_content
	abc
	host:~$ cat abc
	my file contents
```