Add documentation index and source of truth references

README.md

@@ -18,3 +18,41 @@ A custom monitoring and control system for a Nissan Xterra using:
 4. Temperature sensors
 5. JBD/Xiaoxiang BMS integration
 6. Future integrations / optional logging
+
+## Documentation
+
+### Project Status
+
+* `docs/project-state.md`
+* `docs/hardware-status.md`
+
+### System Design
+
+* `docs/architecture.md`
+* `docs/protocol.md`
+* `docs/pico-architecture.md`
+
+### Hardware
+
+* `docs/uart.md`
+* `docs/wiring.md`
+* `hardware/bom.md`
+* `hardware/esp32-pinout.md`
+
+### User Interface
+
+* `docs/ui-wireframes.md`
+
+### Development
+
+These documents should be considered the source of truth for ongoing development.
+
+Priority order:
+
+1. `docs/project-state.md`
+2. `docs/hardware-status.md`
+3. `docs/protocol.md`
+4. `docs/pico-architecture.md`
+5. `docs/ui-wireframes.md`
+
+Implementation should follow documented architecture unless explicitly updated in the documentation first.