docs: add description to commands and index page

cmd/gendocs/gendocs.go

@@ -2,12 +2,13 @@ package gendocs
 
 import (
 	"bytes"
-	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"path"
 	"path/filepath"
 	"strings"
+	"text/template"
 	"time"
 
 	"github.com/rclone/rclone/cmd"
@@ -20,14 +21,25 @@ func init() {
 	cmd.Root.AddCommand(commandDefinition)
 }
 
-const gendocFrontmatterTemplate = `---
-date: %s
-title: "%s"
-slug: %s
-url: %s
-# autogenerated - DO NOT EDIT, instead edit the source code in %s and as part of making a release run "make commanddocs"
+// define things which go into the frontmatter
+type frontmatter struct {
+	Date        string
+	Title       string
+	Description string
+	Slug        string
+	URL         string
+	Source      string
+}
+
+var frontmatterTemplate = template.Must(template.New("frontmatter").Parse(`---
+date: {{ .Date }}
+title: "{{ .Title }}"
+description: "{{ .Description }}"
+slug: {{ .Slug }}
+url: {{ .URL }}
+# autogenerated - DO NOT EDIT, instead edit the source code in {{ .Source }} and as part of making a release run "make commanddocs"
 ---
-`
+`))
 
 var commandDefinition = &cobra.Command{
 	Use:   "gendocs output_directory",
@@ -63,13 +75,36 @@ rclone.org website.`,
 			return err
 		}
 
+		// Look up name => description for prepender
+		var description = map[string]string{}
+		var addDescription func(root *cobra.Command)
+		addDescription = func(root *cobra.Command) {
+			name := strings.Replace(root.CommandPath(), " ", "_", -1) + ".md"
+			description[name] = root.Short
+			for _, c := range root.Commands() {
+				addDescription(c)
+			}
+		}
+		addDescription(cmd.Root)
+
 		// markup for the docs files
 		prepender := func(filename string) string {
 			name := filepath.Base(filename)
 			base := strings.TrimSuffix(name, path.Ext(name))
-			url := "/commands/" + strings.ToLower(base) + "/"
-			source := strings.Replace(strings.Replace(base, "rclone", "cmd", -1), "_", "/", -1) + "/"
-			return fmt.Sprintf(gendocFrontmatterTemplate, now, strings.Replace(base, "_", " ", -1), base, url, source)
+			data := frontmatter{
+				Date:        now,
+				Title:       strings.Replace(base, "_", " ", -1),
+				Description: description[name],
+				Slug:        base,
+				URL:         "/commands/" + strings.ToLower(base) + "/",
+				Source:      strings.Replace(strings.Replace(base, "rclone", "cmd", -1), "_", "/", -1) + "/",
+			}
+			var buf bytes.Buffer
+			err := frontmatterTemplate.Execute(&buf, data)
+			if err != nil {
+				log.Fatalf("Failed to render frontmatter template: %v", err)
+			}
+			return buf.String()
 		}
 		linkHandler := func(name string) string {
 			base := strings.TrimSuffix(name, path.Ext(name))