docs: update .env.example with WireGuard host forwarding and NAT configuration options

Author: x0sina

.env.example

@@ -22,3 +22,9 @@ API_KEY = xxxxxxxx-yyyy-zzzz-mmmm-aaaaaaaaaaa
 # STARTUP_LOG_TAIL_SIZE = 200
 # STATS_UPDATE_INTERVAL_SECONDS = 10
 # STATS_CLEANUP_INTERVAL_SECONDS = 300
+
+### WireGuard optional host forwarding + NAT
+# Set to 0 or false to disable nftables masquerade and sysctl forwarding tweaks.
+# PG_NODE_WG_HOST_ROUTING = 1
+# Egress interface for MASQUERADE; if unset, uses IPv4 default route (then eth0 fallback).
+# PG_NODE_WG_NAT_OUTPUT_INTERFACE = eth0