add example for securing apache config

[voroyam]

WHAT Needs to be Documented?

content-security-policy: default-src 'self'; script-src 'self' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; frame-src *; img-src * data: blob:; font-src 'self' data:; media-src *; connect-src *; base-uri 'self';

WHERE Does This Need To Be Documented (Link)?

https://doc.owncloud.com/server/admin_manual/configuration/server/harden_server.html

WHY Should This Change Be Made?

to give users an example of a secure config