input example should use 'input' and not just 'delta'

[droqen]

https://ambient.run/docs/examples/d563xtcr72ovuuhfkvsgag6z3wiy5jwr

The INPUT example has this line:

let (delta, _input) = input::get_delta();

It does not use _input at all, and this may not be intuitive to first-time users (there was recent confusion in the Discord experienced by @stakso_11721); we should show usage of input because it is common that someone will want to use it for something