docs: re-add troubleshooting section to docs/metrics.md (#129)

#109 deleted the metrics readme, which had a troubleshooting section
that was useful. This PR re-adds that section in `docs/metrics.md`.

Author: MegaRedHand

docs/metrics.md

@@ -72,3 +72,10 @@ The exposed metrics follow [the leanMetrics specification](https://github.com/le
 ---
 
 ✅(*) **Partial support**: These metrics are implemented but not collected "on scrape" as the spec requires. They are updated on specific events (e.g., on tick, on block processing) rather than being computed fresh on each Prometheus scrape.
+
+## Troubleshooting
+
+### Docker Desktop on MacOS
+
+lean-quickstart uses the host network mode for Docker containers, which is a problem on MacOS.
+To work around this, enable the ["Enable host networking" option](https://docs.docker.com/enterprise/security/hardened-desktop/settings-management/settings-reference/#enable-host-networking) in Docker Desktop settings under Resources > Network.