docs(readme): rewrite for someone who arrived from a link

[TMHSDigital]

Everything from the Part 3 review, plus the six additions.

The review's central finding was that 195 words passed before the tool was
positively described, and four terms appeared as if common knowledge: Jev,
JevBench, Benchmark Heaven, cascade. "Decision model", the class of thing
this tool measures, was never defined at all.

Structural

• "What it is" now precedes "What this is not", which stays where it was.
  You cannot appreciate "not a leaderboard" before knowing what the thing is,
  and that framing was previously the entire first screen.
• The argument leads with the real report line as its evidence, instead of
  paraphrasing the same figures as prose bullets and quoting them again sixty
  lines later. The figures appeared twice in two formats and the version with
  authority was the less prominent one.
• bash/zsh quickstart alongside PowerShell, in collapsible sections. CI
  proves Ubuntu works, and most people who would use a Python evaluation tool
  are not on Windows.

Definitions added

decision model, calibration, cascade, Noul, binning noise, and the
Jev wire format. ECE is now explained as a procedure before its floor is
discussed, because the floor argument is unreadable if you do not know what is
being floored.

Overstatements corrected

• "Adding a vendor is config, not code" is now labeled as intent verified
  against one endpoint, linking Add an adapter config for a second Jev-compatible endpoint #11.
• The adapters table gains a "Run for real" column. Two of the three
  transports have never left the test suite (Run the local arm for real: local_logits and generative have never left the test suite #3), and presenting four rows as
  equally available was an omission that functioned as a claim.
• "Windows is the only verified platform" was stale. CI covers Ubuntu.

From the independent review of the rendered page

• --pricing my-pricing.json pointed at a file that never existed. Anyone
  copying it failed on their first paid run. It now shows
  cp docs/pricing.example.json my-pricing.json.
• Prerequisites stated: Python 3.12+ and uv, with a note to check
  python --version, since 3.11 gives a resolver error rather than a message.
• Says plainly it is not on PyPI and that cloning is the install path.
• Maturity note near the top: v0.1.0, one maintainer, API will change in
  v0.2.
• uv sync --extra local documented. Without it the local arm fails every
  case.
• The excerpt no longer leads with the cost line. You were right that it
  read oddly: a seeded mock obviously has no price, so it demonstrated nothing.
  All three quotes now show the tool declining to answer.

Kept on your instruction

"Trustworthy" in the opening line, as a fair summary of calibration plus
discrimination. The GitHub description is aligned to match it.

Verified

All four block quotes checked whitespace-normalised against the committed
report: verbatim. Both internal anchors resolve. No em dashes, no emoji. Gate
green.