add flag for number of refresh workers

flags.go

@@ -40,8 +40,15 @@ var commands = map[string]*flag.FlagSet{
 var (
 	// add
 	addTypeFlag = commands["add"].BoolP(
-		"watch", "w", // long and shorthand flag
-		false, // default
+		"watch", "w",
+		false,
 		`Watch a page instead of adding it as a feed.`,
 	)
+
+	refreshWorkersFlag = commands["refresh"].IntP(
+		"num-workers", "n",
+		5, // 5 workers is a safe default
+		`Number of worker threads to use when refreshing feeds. More is faster,
+but there are more concurrent outgoing requests then.`,
+	)
 )