Update readme.md

Author: shannonmoeller

readme.md

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 # stylelint-config-prettier
 
+> **Note**  
+> As of Stylelint v15 [all style-related rules have been deprecated](https://stylelint.io/migration-guide/to-15#deprecated-stylistic-rules). If you are using v15 or higher and are not making use of these deprecated rules, [this plugin is no longer necessary](https://stylelint.io/migration-guide/to-15#:~:text=Additionally%2C%20you%20may%20no%20longer%20need%20to%20extend%20Prettier%27s%20Stylelint%20config).
+
 [![NPM version][npm-img]][npm-url] [![Downloads][downloads-img]][npm-url]
 
 Turns off all rules that are unnecessary or might conflict with Prettier. This lets you use your favorite shareable config without letting its stylistic choices get in the way when using Prettier.