Say "Wortuhr" where somebody searching for one can read it

[theAndreas]

The repository is public since 2017 and does not appear in a search for its own author's
name plus "Wordclock" — only the profile page does. Five things are missing; three of them
are files and are in here.

Vocabulary. Nearly all search demand in this niche is German — Wortuhr, Wortuhr
ESP32, Wortuhr Selbstbau — and that word appeared nowhere in the repository but
docs/roadmap.md, so the page could not rank for the term its own subject is called by.
The <h1>, the opening paragraph and a short German summary now carry it, together with
the hardware words a builder actually types: WS2812, ESP32-S3, Pico 2 W, NTP, over the air.
The title and the first paragraph are what a search engine shows as the result, so that is
where they had to go rather than into a section further down.

The cold arrival. A stranger landing on the README was sent straight into a table of
directories, which answers a question they had not asked yet. ## What it does comes first
now and says what can be built.

A repository page ranks weakly on its own, so docs/ is made ready to be the project
site: a landing page plus the Jekyll config for jekyll-theme-primer. That theme is the one
GitHub hosts itself — a remote_theme would need a Gemfile and a build step, and nothing
here wants a Ruby toolchain in the repository. No workflow is added for the same reason:
GitHub builds a /docs source by itself.

Nothing new claims a size, so tools/documented-sizes.py has nothing more to check — it
still passes with web/README.md as its only subject.

What this PR cannot do

Two of the five are admin-only fields on the repository and one is off-site, so they stay
with the owner account:

• Topics are empty (topics: []). github.com/topics/wortuhr is a crawled page and the
  main discovery path inside GitHub; without topics the project is not on it. Suggested set:
  wortuhr, wordclock, word-clock, esp32, esp32-s3, rp2350, avr, arduino, ws2812, neopixel, led-matrix, ntp, ota, platformio, cpp17, simulator, wxwidgets, diy, clock, embedded.
• The description is four words — "Wordclock based on Arduino". It is the Google snippet
  and part of the page title, and it has 350 characters available.
• Nothing links here. 0 forks, 2 stars, no mention anywhere; that is the factor Google
  weighs most, and no commit reaches it.

Then Settings → Pages → Source: master /docs, and homepage to the URL it produces.