Support .prettierrc.json5 config file (#8957)

docs/configuration.md

@@ -7,7 +7,7 @@ Prettier uses [cosmiconfig](https://github.com/davidtheclark/cosmiconfig) for co
 
 - A `"prettier"` key in your `package.json` file.
 - A `.prettierrc` file written in JSON or YAML.
-- A `.prettierrc.json`, `.prettierrc.yml`, or `.prettierrc.yaml` file.
+- A `.prettierrc.json`, `.prettierrc.yml`, `.prettierrc.yaml`, or `.prettierrc.json5` file.
 - A `.prettierrc.js`, `.prettierrc.cjs`, `prettier.config.js`, or `prettier.config.cjs` file that exports an object using `module.exports`.
 - A `.prettierrc.toml` file.