docs(readme): convert README.adoc -> Markdown README.md (#29)

README must be real Markdown to render in GitHub community-health, the GitHub
profile, and external MCP directories (Glama) — AsciiDoc shows as raw markup
there. pandoc asciidoc->GFM, badges fixed to clickable, SPDX header kept as an
HTML comment, duplicate README.adoc removed.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -0,0 +1,80 @@
+<!--
+SPDX-License-Identifier: CC-BY-SA-4.0
+SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+-->
+
+Rust parser and renderer for K9 self-validating configuration files —
+declares software components with provenance tracking, security
+classification, build recipes, and runtime contracts.
+
+# Overview
+
+K9 is a configuration format for software component declarations. Each
+component carries:
+
+- **Pedigree** — provenance: origin URL, author, license, supply-chain
+  hashes
+
+- **SecurityLevel** — Kennel / Yard / Hunt (same three-tier model as K9
+  Nickel components)
+
+- **Recipe** — build or assembly instructions (tool + command)
+
+- **Contracts** — runtime invariants with check commands and severity
+  levels
+
+`k9-rs` supports two surface formats:
+
+- `.k9` — YAML-like plain-text format parsed natively
+
+  \* `.k9.ncl` — Nickel format; detected and returned as \`K9Error  
+  NickelFormat\` (requires the Nickel evaluator — use `pandoc-k9` for
+  Nickel K9 files)
+
+  == Quick Start
+
+```rust
+use k9_svc::parser::parse;
+use k9_svc::renderer::render;
+
+let input = r#"component: my-svc
+  version: 0.1.0
+  pedigree:
+    origin: https://github.com/example/svc
+    author: Alice
+  security: kennel
+"#;
+
+let components = parse(input)?;
+let output = render(&components)?;
+```
+
+# Security Levels
+
+| Level | Meaning |
+|----|----|
+| `kennel` | Data-only. No execution. Strict sandbox. Safe to parse anywhere. |
+| `yard` | Nickel evaluation + limited I/O. Capability-based sandbox. |
+| `hunt` | Full shell execution via recipes. Cryptographic signature required. |
+
+# Modules
+
+| Module     | Purpose                                                        |
+|------------|----------------------------------------------------------------|
+| `types`    | `Component`, `Pedigree`, `SecurityLevel`, `Recipe`, `Contract` |
+| `parser`   | `parse(str)` `→` `Vec<Component>` — detects Nickel format      |
+| `renderer` | `render(&[Component])` `→` `String`                            |
+| `error`    | `K9Error`: `ParseError`, `NickelFormat`, `Io`, `RenderError`   |
+
+# Related
+
+- [k9-haskell](https://github.com/hyperpolymath/k9-haskell) — Haskell
+  implementation
+
+- [pandoc-k9](https://github.com/hyperpolymath/pandoc-k9) — Pandoc
+  reader/writer for `.k9.ncl` files
+
+# License
+
+MPL-2.0 (MPL-2.0 preferred; MPL-2.0 required for crates.io). See
+[LICENSE](LICENSE).