Tell users how not to use volumes

[Al2Klimov]

refs #45

[mcktr]

I strongly disagree on this pull request. This does not fix the problem at all and is from a user perspective a very bad solution, the consequence is that you have to start the container once without any configuration file!

The container already contains a custom build Go entrypoint binary, why not detect programmatically if it is the very first startup or not? If it is the very first startup the Go entrypoint can the create the directories or let the Icinga 2 daemon create the directories.

Best regards
Michael

[julianbrost]

I wouldn't see this PR as a fix for the corresponding issue, but rather a documentation of an unfortunate pitfall with no real solution.

So remove the "fixes" and I'm fine with this for now as it is still better than the status quo and to me there so obvious simple solution to the actual problem (I'll comment more on this in the issue in a second).