Update syslog documentation

[guruOS1]

There is a typo of option: “syslog=udp://1.2.3.4:1111” should be “syslog-address=udp://1.2.3.4:1111”

[joaofnfernandes]

This seems to be right, but while we're at it, @thaJeztah in this page we also have the equivalent config for the daemon.json file. Do you mind checking if it is correct, and what other properties are supported for the syslog driver?

[thaJeztah]

The daemon.json should accept the same options as --log-opt (they're parsed by the same code)