docs: narzedzie na stronie, przez ktora wchodzi caly serwis - #247

Checked rather than assumed, and the result was worse than expected: the docs
homepage mentioned zerosmtp-check zero times, npx zero times, and linked to none
of the seventeen per-error pages. It is the entry point for the site and it knew
nothing about two days of work.

Same failure as the orphan pages and the README earlier today, in a third place:
the thing gets built and does not appear where people land.

It goes above the triage table rather than becoming a seventeenth row in it. The
table answers "which page do I need", which is the right question when you are
reading. Somebody mid-incident with an error on screen has a different one, and
for them a single command beats picking from sixteen options - especially since
the string they are looking at is usually not what the server sent, which is the
part no page can tell them by being well organised.

The hanging case is named separately because it is the most common first
failure and it is not an authentication problem at all: the network is refusing
the port, and no amount of reading about 5.7.139 will say so.