Update lint-staged example to use node.js path (#30510)

The current example attempts to remove resolve the relative pathname of the absolute pathnames given by `lint-staged` using string manipulation and `process.cwd()`. This is a risky solution because pathnames have many platform dependent edge cases. The example also returns pathnames that are technically wrong in linux. `/home/project/file => /file`,

I propose to use the utilities provided by node.js to resolve the relative pathnames, and to format the sample `.lintstagedrc.js` file in a manner easier for novice programmers to understand and modify.



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [x] Make sure the linting passes by running `yarn lint`

Author: mi-na-bot

docs/basic-features/eslint.md

@@ -203,11 +203,15 @@ Then, add `prettier` to your existing ESLint config:
 If you would like to use `next lint` with [lint-staged](https://github.com/okonet/lint-staged) to run the linter on staged git files, you'll have to add the following to the `.lintstagedrc.js` file in the root of your project in order to specify usage of the `--file` flag.
 
 ```js
+const path = require('path')
+
+const buildEslintCommand = (filenames) =>
+  `next lint --fix --file ${filenames
+    .map((f) => path.relative(process.cwd(), f))
+    .join(' --file ')}`
+
 module.exports = {
-  '**/*.js?(x)': (filenames) =>
-    `next lint --fix --file ${filenames
-      .map((file) => file.split(process.cwd())[1])
-      .join(' --file ')}`,
+  '*.{js,jsx,ts,tsx}': [buildEslintCommand],
 }
 ```