add struct field comment

Author: salonichf5

internal/controller/nginx/config/http/config.go

@@ -120,7 +120,7 @@ const (
 // Upstream holds all configuration for an HTTP upstream.
 type Upstream struct {
 	Name                string
-	ZoneSize            string
+	ZoneSize            string // format: 512k, 1m
 	StateFile           string
 	LoadBalancingMethod string
 	KeepAlive           UpstreamKeepAlive