docs: add minimum versions to the command pages

cmd/serve/restic/restic.go

@@ -128,6 +128,9 @@ these **must** end with /.  Eg
 The` + "`--private-repos`" + ` flag can be used to limit users to repositories starting
 with a path of ` + "`/<username>/`" + `.
 ` + httplib.Help,
+	Annotations: map[string]string{
+		"versionIntroduced": "v1.40",
+	},
 	Run: func(command *cobra.Command, args []string) {
 		cmd.CheckArgs(1, 1, command, args)
 		f := cmd.NewFsSrc(args)