docs: Add note to tutorial about ufs get/put only operating on one file.

For example, "ufs put hello.py main.py" will not copy two files but instead
will copy hello.py and save it as main.py on the remote filesystem.

docs/tutorials/storage.rst

@@ -217,6 +217,9 @@ Finally, the ``put`` sub-command puts a file from your computer onto the
 connected device (it's named after the ``put`` command that's part of FTP that
 serves the same function).
 
+.. note::
+    The ufs get and put commands only operate on one file at a time.
+
 Mainly main.py
 ++++++++++++++