* Change 13.0 references to 14.0
* Change Ubuntu version to 20.04 as it was the stable version at Odoo
release time
* Remove unnecessary postgresql pre-installation as Debian and Ubuntu
install the recommended packages by default
* Replace `root` commands by `sudo` commands as it's the preferred way
to run admin commands
* Remove the manual installation of xlwt and num2words as the Debian
packages now exist.
* Bump the supported Fedora version to Fedora 32.
* Add a warning about unsupported Fedora 33 (because of Python 3.9 that
would need a separate package)
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