Improve text of gossec alert

[cubranic]

The current text of the alert is not helpful enough to the tsar:

Gossec does not seem to be running on wind. Please assess its status and check the logs on wind with tail /var/log/gossec.log, and then ask @sysadmin or @tristan to rectify the issue.

A more helpful alert would mention instructions in the wiki, at least: https://bao.chimenet.ca/wiki/index.php/Gossec_Manual#Problem_files

[ketiltrout]

Gossec does not seem to be running on wind. Often this is due to gossec failing to process problem files. Try to identify and clean them up: https://bao.chimenet.ca/wiki/index.php/Gossec_Manual#Problem_files . If that doesn't work, ask @sysadmin or @tristan for help.

[cubranic]

Deployed.