Rewrite README for public hardening

[s00ly]

What changed

• Rebrands the public project as NomadPosting while documenting the legacy IVPN_* prototype prefix.
• Leads with the dry-run-only safety boundary and removes claims that could imply working live privacy protection.
• Adds a concise purpose, privacy/non-goal table, evidence-backed status matrix, contributor hardening tracks, and orange/purple/graphite target architecture.
• Replaces the broken fresh-clone build path with verified Bash and PowerShell dry-run commands.
• Corrects the relay-review and full-database-encryption overclaims.
• Links the newly enabled private vulnerability reporting channel and records the successful Linux CI race run.
• States the licensing gap plainly: public source is not legally open source until the owner selects a license.

Why

The original README was credible but optimized for auditors rather than first-time contributors. It also used an internal prototype name, buried the contribution path, and overstated two controls. This rewrite aims to attract privacy and security reviewers through a memorable purpose, concrete work, and honest evidence rather than hype.

Verification

• GitHub Markdown API rendered the README successfully.
• Every relative README link resolves locally.
• The documented development configuration passed go run ./cmd/ivpn --check with a fresh generated key and temporary database.
• go test -count=1 ./...
• go vet ./...
• go mod verify
• gofmt -l cmd internal returned no files.
• Credential-pattern scan returned no matches.

Maintainer decision still required

Select an OSI-approved license before describing the repository as open source or accepting code contributions. AGPL-3.0-or-later is the reciprocal freedom-tech option; Apache-2.0 is the adoption-first option.