feat(docs): wpis urzadzenia moze wskazac swoj szczegolowy poradnik - #260

HP now has two pages: the generated compatibility entry, which is a row of
facts with the vendor's statement behind it, and HP-PRINTER-SMTP.md, which
explains what "SMTP server requires authentication" means and what to do about
each of its three causes. Nothing connected them, so a reader who found the
compatibility row got the status and no way forward.

The generator renders the link only where an entry names one. That condition
matters: a "further reading" line pointing at a page covering ten brands is not
further reading, it is the same link the Related section already carries, and
adding it everywhere would be link-stuffing our own site rather than helping
anybody.

Which is also why this is one link and not thirty-four. The tempting version
was to add the new focused pages to the Related section on every generated
page - three inbound links each becomes thirty-four, and the numbers look
better. A reader on the page for 5.7.233, a tenant daily sending limit, gains
nothing from a link to an HP printer guide. Internal links help when they are
the link somebody wanted next.