Bug#871490: mention how to force listing of /var/lib/systemd/coredump

[積丹尼 Dan Jacobson]

Yes mine do get cleaned out eventually by cron etc.

I'm just unhappy about

NAME
       coredumpctl - Retrieve and process saved core dumps and metadata

       -1
           Show information of a single core dump only, instead of listing all
           known core dumps.                                               ^^^
           ^^^^^^^^^^^^^^^^^
I mean even ls(1) knows about more coredumps!

It is only when one reads the fine print and all related man pages, does
one find out why it is "broken".

It should say why earlier.