add comment to deprecate and prevent new use-cases for pkg/ssh

Signed-off-by: Andrew Sy Kim <kim.andrewsy@gmail.com>

pkg/ssh/ssh.go

@@ -14,6 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+// WARNING: DO NOT add new use-caes to this package as it is deprecated and slated for deletion.
+
 package ssh
 
 import (