CONTRIBUTING.md for outside contributors; README status and a Contributing section

Refs #7

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

@@ -8,9 +8,11 @@ storytold "craft" family.
 
 ![SolveCraft with the sample plate](docs/screenshots/sample-plate.png)
 
-**Status: early (milestone M0 done, M1 in progress).** See [ROADMAP.md](ROADMAP.md),
-[docs/parity.md](docs/parity.md) (command parity with Fusion's Design workspace) and
-[docs/oracle.md](docs/oracle.md) (parts built in Fusion, rebuilt and measured in SolveCraft).
+**Status: early but usable for simple parts.** 76 of 76 reference parts built in Fusion
+rebuild in SolveCraft with the same volume, area and topology ([docs/oracle.md](docs/oracle.md));
+command parity with Fusion's Design workspace is tracked in [docs/parity.md](docs/parity.md).
+Open work and known bugs are in [GitHub issues](https://github.com/bherbruck/solvecraft/issues),
+and help is welcome: see [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## What works
 
@@ -98,6 +100,11 @@ configuration and an example session: [docs/mcp.md](docs/mcp.md).
 | L5 | `ui-egui`, `mcp` | the swappable desktop front end; the MCP server (headless or bridged to the app) |
 | apps | `solvecraft`, `solvecraft-cli` | desktop app, headless CLI |
 
+## Contributing
+
+See [CONTRIBUTING.md](CONTRIBUTING.md): how to build and test, the code map, the clean-room
+and licence rules, and where help is wanted most.
+
 ## Licence
 
 MIT OR Apache-2.0, at your option. SolveCraft is not affiliated with Autodesk; Fusion is a