Fix old documentation sugesting use of 'git worktree'

#!/usr/bin/env bash

#

# Copyright 2018 Dominik Sekotill

# Copyright 2018-2019, 2022 Dominik Sekotill

#

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

  from there.  In 'super working trees' the repository is stored in the

  top-level directory and each working tree (including the main one) is a

  subdirectory. New working trees can be created from the top-level with the

  \`git worktree add\` command.

  \`git supertree add\` command.

$SCRIPT init [WORKTREE-BASE] [-b BRANCH[:PATH]]