Add small script to setup label in lesson repo

@gvwilson Do you approve this?

@willingc If @gvwilson approve this, could you review it?
`sed 's/##//g'` will leave the lines begin with white-space and `sed 's/^## //g'` will not match some lines since they don't end with white-space. I tried `sed 's/^##?//'` but it didn't work.