adding some documentation and additional output for pagerduty provider

The config.php.example simply adds some documentation around using the apikey for auth.
I also added some additional output for the pagerduty.php oncall provider. Before, it only had the pagerduty trigger url, which forced you to click through. This also adds output from trigger_summary_data. While not pretty, it does add more context.

Example of output from prior to change:
https://mycompany.pagerduty.com/incidents/XXXX/log_entries/YYYYY

Example of output post change:
https://mycompany.pagerduty.com/incidents/XXXX/log_entries/YYYYY
{
    "pd_description": "<something pagerduty has here>",
    "pd_nagios_object": "service",
    "HOSTNAME": "myhostname",
    "SERVICEDESC": "myservice",
    "SERVICESTATE": "CRITICAL"
}