Add section on Aristo to CONTRIBUTING.md

Author: penberg

CONTRIBUTING.md

@@ -413,6 +413,19 @@ And launch an Antithesis test run with:
 scripts/antithesis/launch.sh
 ```
 
+## Annotating intent with Aristo
+
+Turso uses [Aristo](https://github.com/aretta-ai/aristo) to capture design intent that the code alone doesn't spell out — invariants a refactor could silently break — as `#[aristo::intent("...")]` annotations attached to the code. They're optional; reach for one only when a property is invisible from the signature and not already guarded by a test.
+
+The macros are a workspace dependency, so annotated code builds normally. To author and lint annotations, install the CLI:
+
+```console
+cargo install aristo-cli   # provides the `aristo` command
+aristo lint                # lint annotation prose (also runs in CI on every PR)
+```
+
+To machine-check annotations, run `/aristo-neural-verify` in Claude Code.
+
 ## Adding Third Party Dependencies
 
 When you want to add third party dependencies, please follow these steps: