Add help text to subcommands.

This way they appear better in the console.

code/iottb/subcommands/add_device.py

@@ -10,7 +10,8 @@ logger.setLevel(logging.INFO)  # Since module currently passes all tests
 
 
 def setup_init_device_root_parser(subparsers):
-    parser = subparsers.add_parser('add-device', aliases=['add-device-root', 'add'])
+    parser = subparsers.add_parser('add-device', aliases=['add-device-root', 'add'],
+                                   help='Initialize a folder for a device.')
     parser.add_argument('--root_dir', type=pathlib.Path, default=pathlib.Path.cwd())
     group = parser.add_mutually_exclusive_group()
     group.add_argument('--guided', action='store_true', help='Guided setup', default=False)