Add usage sample for Yarn to README

[Tomalak]

When using Yarn in PnP mode (the default) as the package manager, trying the documented run command

npx @eslint/config-inspector@latest

fails with an error message along the lines of the following:
(also note that it always says eslint.config.js, even if it's actually e.g. eslint.config.mjs)

Failed to load `eslint.config.js`.
https://eslint.org/docs/latest/use/configure/configuration-files-new
Error [ERR_MODULE_NOT_FOUND]: Cannot find package 'globals' imported from C:\config-inspector-test\eslint.config.bundled_dso4w158dx.mjs  
    at new NodeError (node:internal/errors:406:5)
    at moduleResolve (node:internal/modules/esm/resolve:838:20)
    at defaultResolve (node:internal/modules/esm/resolve:1043:11)
    at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:383:12)
    at ModuleLoader.resolve (node:internal/modules/esm/loader:352:25)
    at ModuleLoader.getModuleJob (node:internal/modules/esm/loader:228:38)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/module_job:85:39)
    at link (node:internal/modules/esm/module_job:84:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

because npx has no idea how to resolve Yarn packages.

The way to successfully run it with Yarn would be

yarn add -D @eslint/config-inspector

and then

yarn run config-inspector

which would be a helpful addition to the usage section of the README.

[antfu]

Would you like to send a quick PR for that? Thanks