More secure Dockerfile

[kugland]

• Drop privileges and run as nobody:nobody.
• Chroot into /var/www/htdocs.
• Compile with hardening options.

(Tested on x86-64 and aarch64.)

[kugland]

What you think of adding a mimetypes file to the Docker image?

[emikulic]

Up to you re: mimetypes. :)