[RPKI] Krill install-and-run doc update

[John Kristoff]

Hello NLnet Labs,

Apparently the doc here:

  <https://krill.docs.nlnetlabs.nl/en/stable/install-and-run.html>

has some problems.  There doesn't appear to be any actual Debian amd64
packages for example.

I'd submit a doc patch, but this might be a little more involved for me
to figure out exactly what you should say.  Maybe just point to your
standalone Debian sources or is there another preferred method for this
architecture?

Thank you,

John