docs: reword cloudflare-workers section on service worker mode vs module worker mode

[WillSmithTE]

put module workers first since they're the recommended way move justification into the same paragraph to make sure it gets read

I had the same problem as this commenter. To me, this is clearer and points users more clearly to the happy path

[yusukebe]

@WillSmithTE

You are right. This should be first. Thanks!