docs: clarify ARP flux sysctl limitations with host networking

install/production-filesystem/entrypoint.d/37-host-optimization.sh

@@ -22,6 +22,9 @@ if [ "$failed" -eq 1 ]; then
       net.ipv4.conf.all.arp_ignore=1
       net.ipv4.conf.all.arp_announce=2
 
+    Note: If using 'network_mode: host', you cannot set these via docker-compose
+    sysctls. You must configure them directly on your host operating system instead.
+
     Detection accuracy may be reduced until configured.
 
     See: https://docs.netalertx.com/docker-troubleshooting/arp-flux-sysctls/