Add ADB logging documentation to DEVELOPMENT.md

DEVELOPMENT.md

@@ -108,3 +108,29 @@ Important: **Billing only works reliably when the app is installed from Google P
 6. **Verify in the app**
    - Trigger the subscribe/buy flow and confirm the purchase dialog appears.
    - Confirm acknowledgements/entitlements are applied as expected.
+
+
+## Billing logging (ADB)
+
+Billing logs are written to Android's system log (Logcat), not displayed in the app UI.
+
+To view billing logs:
+
+```bash
+# View only MindMachine billing logs
+adb logcat -s MindMachineBilling:D
+
+# Filter with silence for other tags
+adb logcat -s MindMachineBilling:D *:S
+```
+
+Example log lines you'll see:
+- `Billing setup finished: 0 OK`
+- `Product details loaded: 2 items`
+- `Query purchases returned X items`
+- `Active entitlement: true/false`
+- `Entitlement changed: false -> true`
+
+Billing log tags:
+- `MindMachineBilling` for debug/info messages
+- Errors use `Log.e()` and appear as `E/MindMachineBilling` in logcat