Update usage.md

[jaysonng]

For await to work, it needs to be inside an async function. or else an error will occur

SyntaxError: await is only valid in async functions and the top level bodies of modules

[mtrezza]

That's only true for old Node.js versions

[jaysonng]

interesting. I'm running node 18.

is that for node 20? and what can we do you think to add to these docs for subtle differences in node version code?