Make the usage message a bit more informative

go/remind/remind.go

@@ -27,6 +27,21 @@ var flags struct {
func init() {
	flag.BoolVar(&flags.showAll, "all", false, "Show all reminders")
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "%s <cmd>\n", os.Args[0])
		fmt.Fprintln(os.Stderr)
		fmt.Fprintf(os.Stderr, "Available commands:\n")
		fmt.Fprintf(os.Stderr, "  add  <date> <description>\n")
		fmt.Fprintf(os.Stderr, "  list <when>\n")
		fmt.Fprintf(os.Stderr, "    where `when` is empty or one of: today\n")
		fmt.Fprintf(os.Stderr, "  l    (alias for `list`)\n")
		fmt.Fprintln(os.Stderr)
		flag.PrintDefaults()
	}
}
func isCommand(s string) bool {
	return s == "list" || s == "l" || s == "add"
}