Simplify Caddy reverse proxy example by using transparent shorthand

[MarkOtzen]

Instead of manually adding headers, one can use the transparent shorthand. This is equivalent to

header_upstream Host {host}
header_upstream X-Real-IP {remote}
header_upstream X-Forwarded-For {remote}
header_upstream X-Forwarded-Proto {scheme}

which is a superset of the current configuration while being shorter and clearer.

https://caddyserver.com/docs/proxy

[astorije]

Hey @MarkOtzen, thanks for your first PR and welcome to The Lounge!
If you're interested, feel free to request some stickers at https://goo.gl/forms/f5usqAEp5DWoeXC92 🙂

[MarkOtzen]

Thanks for the offer, but I already got a set. 😉