Update 01 Felix and Herbert.md

Clarifications for New Starters as the terms were unclear, especially that you were creating two sets of scripts.
Agreed **stage backdrop** not quite right, suggest **stage** sprite in backdrop pane.  - might be better description. Although the Backdrop pane is not explicitly defined by MIT - only the Sprite Pane is defined.

So may need to use **stage** sprite in Sprite Pane.