update docs to signify that php-server serves from ./public directory by default, add translations of doc blocks that were missed in previous pr's

[henderkes]

#1571 accidentally pushed the frankenphp directive to the main branch, so restoring this one under another branch

[dunglas]

I'm not in favor of printing a warning. To me, the current behavior is expected and desirable when using the embedded app feature.

[henderkes]

Okay. It definitely confused me when I tested the embedded app bug someone reported. I only figured it out when I enabled logging in the Caddyfile and figure out that it was trying to serve from a non-existent public directory.

I'll remove the code changes, but keep the documentation bits.