add some description of xl.meta (#9901)

docs/bucket/versioning/xl-meta-to-json.go

@@ -1,3 +1,19 @@
+/*
+ * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package main
 
 import (
@@ -18,7 +34,18 @@ func main() {
 	app := cli.NewApp()
 	app.Copyright = "MinIO, Inc."
 	app.Usage = "xl.meta to JSON"
-	app.Version = "0.0.1"
+	app.HideVersion = true
+	app.CustomAppHelpTemplate = `NAME:
+  {{.Name}} - {{.Usage}}
+
+USAGE:
+  {{.Name}} {{if .VisibleFlags}}[FLAGS]{{end}} METAFILES...
+{{if .VisibleFlags}}
+GLOBAL FLAGS:
+  {{range .VisibleFlags}}{{.}}
+  {{end}}{{end}}
+`
+
 	app.HideHelpCommand = true
 
 	app.Flags = []cli.Flag{
@@ -29,6 +56,10 @@ func main() {
 	}
 
 	app.Action = func(c *cli.Context) error {
+		if !c.Args().Present() {
+			cli.ShowAppHelp(c)
+			return nil
+		}
 		for _, file := range c.Args() {
 			var r io.Reader
 			switch file {