docs(README): Add section on running tests and writing test examples

Author: roxblnfk

README.md

@@ -56,6 +56,66 @@ return new ApplicationConfig(
 );
 ```
 
+### Running Tests
+
+To run your tests, execute:
+
+```bash
+vendor/bin/testo
+```
+
+### Writing Your First Test
+
+Create a test class in the configured test directory (e.g., `tests/CalculatorTest.php`):
+
+```php
+<?php
+
+declare(strict_types=1);
+
+namespace Tests;
+
+use Testo\Assert;
+use Testo\Attribute\Test;
+use Testo\Attribute\RetryPolicy;
+use Testo\Attribute\ExpectException;
+
+final class CalculatorTest
+{
+    #[Test]
+    public function dividesNumbers(): void
+    {
+        $result = 10 / 2;
+
+        Assert::same(5.0, $result);
+        Assert::notSame(5, $result); // Types matter!
+    }
+
+    #[Test]
+    #[RetryPolicy(maxAttempts: 3)]
+    public function flakyApiCall(): void
+    {
+        // Retries up to 3 times if test fails
+        $response = $this->makeExternalApiCall();
+
+        Assert::same(200, $response->status);
+    }
+
+    #[Test]
+    #[ExpectException(\RuntimeException::class)]
+    public function throwsException(): void
+    {
+        throw new \RuntimeException('Expected error');
+    }
+}
+```
+
+What to note:
+- Use the `#[Test]` attribute to mark test methods
+- Test classes don't need to extend any base class
+- Use `Assert` class for assertions (`same`, `true`, `false`, `null`, `contains`, `instanceOf`, etc.)
+- Testo provides multiple attributes to extend testing capabilities (retry policies, exception handling, and more)
+
 ## IDE Support
 
 Testo comes with the [IDEA plugin `Testo`](https://plugins.jetbrains.com/plugin/28842-testo?noRedirect=true).