crontab.5 man page

systemd-crontab-generator should also include a crontab.5 describing the layout of crontabs file.

This is take almost verbatim from the vixie-cron present in Debian Stable (raspbian),
I only commented some Debian-specific changes.

"./On the Debian GNU/Linux system, cron supports the  ./.B pam_env ...."  ->   lines starting with .\ are comments.

Does systemd-crontab-generator includes this ?
I don't think it's really needed to be 100% bug compatible; 
as long as it is stated in the manpage.

+.SH DIAGNOSTICS
+cron requires that each entry in a crontab end in a newline character. If the
+last entry in a crontab is missing a newline (ie, terminated by EOF), cron will
+consider the crontab (at least partially) broken. A warning will be written to
+syslog.