readme: for the person who finds the repository public

[aledbf]

The README was written while the repository was private. Rewritten for whoever reads it first now:

Wrong, fixed

• The install example named 20261005.1, which dl.constructlinux.org no longer lists (404 for whoever copied it); the version is now read from SHA256SUMS' first line.
• "about 110 recipes": 208. task keygen:release alone: task usb needs the PCR and Secure Boot keys too.
• The extensions list, the apps (Ghostty, VS Code, Tailscale, CUPS, OpenSSH were missing), the Layout table (internal/ has 16 packages, cmd/construct 13 commands) - the table is gone, AGENTS.md has it.
• "Erases the first internal disk" was in the section after the install steps; it is now in "What it needs", first.

Added

• A screenshot (docs/desktop.png, from the harness).
• What the project's state is: days old, CalVer, testing then stable.
• Requirements: x86-64-v3, UEFI only, GPU drivers, TPM optional, a 16 GB stick, a whole disk; and what is not here.
• Living with it: the password and the TPM, the recovery key, a security key and a fingerprint, channels and the update notice, the factory reset, construct report/diagnose, SECURITY.md.
• What a release ships (signed sums, SBOM, Grype), and where fixes to the forks go.

Removed

• "Test it" and "Layout": contributor material duplicating AGENTS.md, already drifted. Four lines point there.
• "The stick", which retold Install.

task check passes. One naming note not in this PR: SECURITY.md says CONSTRUCT, os-release and the README say Construct.

🤖 Generated with Claude Code