mbed-os-to-arduino-macos prerequisites incorrect

The list:

```
###########################################################################################
# mbed-os-to-arduino (macOS Version)
#
# This is an adapted version of the original 'mbed-os-to-arduino' script
# specifically tailored for macOS systems.
#
# Prerequisites:
# - jq (Installation: brew install jq)
# - rsync (Installation: brew install rsync)
# - gcc-arm-embedded (Installation: brew install gcc-arm-embedded)
# - hg (Installation: brew install hg)
# - bash (Installation: brew install bash)
# - python (Installation: brew install python)
# - gnu-utils (Installation: brew install gnu-utils)
# - gnu-sed (Installation: brew install gnu-sed)
# - coreutils (Installation: brew install coreutils)
# - ArduinoCore-mbed requirements (Installation: pip install -r requirements.txt)
```

1. There is no requirements.txt file. See https://github.com/search?q=repo%3Aarduino%2FArduinoCore-mbed%20requirements.txt&type=code
2. There is no gnu-utils cask:
```
(base) andy@ice ArduinoCore-mbed % brew install gnu-utils
Warning: No available formula with the name "gnu-utils". Did you mean gnu-units, num-utils, gnutls, gnu-time, gputils or uniutils?
==> Searching for similarly named formulae and casks...
==> Formulae
gnu-units num-utils gnutls ✔ gnu-time gputils uniutils

To install gnu-units, run:
brew install gnu-units
```

It would appear requirements.txt is generated after I've installed `mbed-cli` and then run the mbed-os-to-arduino-macos script which fails due to missing packages but generating a requirements.txt. I think the pre-reqs and the docs on the front page are assuming more contextual knowledge than is reasonable.