Readme needs required Chef version bumping to 16.0+

[KillerCars]

:speaking_head: Foreword

Thank for taking the time to fill this bug report fully. Without it we may not be able to fix the bug, and the issue may be closed without resolution.

:ghost: Brief Description

A clear and concise description of what the bug is.

README.md shows Chef 15.3+, but should be 16.0+

:pancakes: Cookbook version

Version of the cookbook where you are encountering the issue.

v10.0.0+

:woman_cook: Chef-Infra Version

Version of chef-client in your environment.

15.14

:tophat: Platform details

Operating system distribution and release version. Cloud provider if running in the cloud.

Steps To Reproduce

Steps to reproduce the behavior:

1. Go to 'README.md'
2. Scroll down to 'https://github.com/sous-chefs/postgresql#chef'
3. Look with your eyes
4. See error

:police_car: Expected behavior

A clear and concise description of what you expected to happen.

Should read '16.0+'

:heavy_plus_sign: Additional context

Add any other context about the problem here. e.g. related issues or existing pull requests.