Update README.md

Author: e1himself

README.md

@@ -1,2 +1,40 @@
-# null-container
-Null (always empty) PSR-11 container implementation
+# NullContainer
+
+`NullContainer` is a [PSR-11](https://www.php-fig.org/psr/psr-11/) container implementation that is always empty. 
+
+This is useful when you want to provide an optional `ContainerInterface` dependency, 
+but don't want to deal with nullable values.
+
+## Features
+
+- PSR-11
+- PHP 7.0+
+- PHP 8.0
+- Semver
+- Tests
+
+## Example
+
+```php
+use Psr\Container\ContainerInterface;
+use Technically\NullContainer\NullContainer;
+
+final class MyServiceContainer implements ContainerInterface
+{
+    private ContainerInterface $parent;
+
+    /**
+     * @param ContainerInterface|null $parent
+     */
+    public function __construct(ContainerInterface $parent = null)
+    {
+        $this->parent = $parent ?? new NullContainer();
+    }
+
+    // ... your code, where you don't need to deal with $parent set to `null`.
+}
+```
+
+## Credits
+
+- Implemented by [Ivan Voskoboinyk](https://github.com/e1himself)