added readme.md

Author: dg

readme.md

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+# PHPStan extensions for Nette libraries
+
+![Nette PHPStan Rules](https://github.com/user-attachments/assets/c231ed47-a413-4dd2-81ef-83e52c080427)
+
+[![Downloads this Month](https://img.shields.io/packagist/dm/nette/phpstan-rules.svg)](https://packagist.org/packages/nette/phpstan-rules)
+[![Tests](https://github.com/nette/phpstan-rules/workflows/Tests/badge.svg?branch=master)](https://github.com/nette/phpstan-rules/actions)
+[![Latest Stable Version](https://poser.pugx.org/nette/phpstan-rules/v/stable)](https://github.com/nette/phpstan-rules/releases)
+[![License](https://img.shields.io/badge/license-New%20BSD-blue.svg)](https://github.com/nette/phpstan-rules/blob/master/license.md)
+
+ <!---->
+
+<h3>
+
+Makes [PHPStan](https://phpstan.org) smarter about Nette code. Install, and it just works — more precise types, fewer false positives.
+
+</h3>
+
+ <!---->
+
+
+## Installation
+
+Install via Composer:
+
+```shell
+composer require --dev nette/phpstan-rules
+```
+
+Requirements: PHP 8.1 or higher and PHPStan 2.1+.
+
+If you use [phpstan/extension-installer](https://github.com/phpstan/extension-installer), the extension is registered automatically. Otherwise add to your `phpstan.neon`:
+
+```neon
+includes:
+    - vendor/nette/phpstan-rules/extension.neon
+```
+
+ <!---->
+
+## What's Included
+
+ <!---->
+
+**Precise return types** — narrows return types of `Strings::match()`, `matchAll()`, `split()`, `Helpers::falseToNull()`, and `Expect::array()` based on the arguments you pass.
+
+**Removes `|false` from PHP functions** — functions like `getcwd`, `json_encode`, `preg_split`, and [many more](extension-php.neon) return `string|false` even though `false` is unrealistic on modern systems.
+
+**Assert type narrowing** — PHPStan understands type guarantees after `Tester\Assert` calls like `notNull()`, `type()`, `true()`, etc.
+
+**False positive suppression** — silences known PHPStan false positives in Nette patterns (arrow functions passed as `void` callbacks, runtime type validation closures).
+
+ <!---->
+
+### Type Assertion Testing Helper
+
+For Nette package developers: `TypeAssert` lets you verify type inference in tests using [Nette Tester](https://tester.nette.org):
+
+```php
+use Nette\PHPStan\Tester\TypeAssert;
+
+TypeAssert::assertTypes(__DIR__ . '/data/types.php', [__DIR__ . '/../extension.neon']);
+```
+
+The data file uses `assertType()` from PHPStan:
+
+```php
+use function PHPStan\Testing\assertType;
+
+assertType('non-empty-string', getcwd());
+assertType('string', Normalizer::normalize('foo'));
+```
+
+ <!---->
+
+## [Support Me](https://github.com/sponsors/dg)
+
+Do you like Nette? Are you looking forward to the new features?
+
+[![Buy me a coffee](https://files.nette.org/icons/donation-3.svg)](https://github.com/sponsors/dg)
+
+Thank you!