Readme update

ReadMe.md

@@ -19,3 +19,40 @@ Alternative setup composer local zip file repot:
 ## Install package
 
 `composer require egrajp/exceptions-extended`
+
+## PHP Exception model
+
+Here's a chart that demonstrates the new hierarchy introduced in PHP 7:
+
+```txt
+\Throwable
+├── \Exception (implements \Throwable)
+|   |── \DOMException (extends \Exception)
+|   ├── \IntlException (extends \Exception)
+|   ├── \JsonException (extends \Exception)
+|   |── \PharException (extends \Exception)
+|   |── \ReflectionException (extends \Exception)
+|   |── \ValueError (extends \Exception)
+│   ├── \LogicException (extends \Exception)
+│   │   ├── \BadFunctionCallException (extends \LogicException)
+│   │   │   └── \BadMethodCallException (extends \BadFunctionCallException)
+│   │   ├── \DomainException (extends \LogicException)
+│   │   ├── \InvalidArgumentException (extends \LogicException)
+│   │   ├── \LengthException (extends \LogicException)
+│   │   └── \OutOfRangeException (extends \LogicException)
+│   └── \RuntimeException (extends \Exception)
+│       ├── \OutOfBoundsException (extends \RuntimeException)
+│       ├── \OverflowException (extends \RuntimeException)
+│       ├── \RangeException (extends \RuntimeException)
+│       ├── \UnderflowException (extends \RuntimeException)
+│       └── \UnexpectedValueException (extends \RuntimeException)
+└── \Error (implements \Throwable)
+    ├── \AssertionError (extends \Error)
+    ├── \ParseError (extends \Error)
+    └── \TypeError (extends \Error)
+        └── \ArgumentCountError (extends \TypeError)
+    └── \ArithmeticError (extends \Error)
+        └── \DivisionByZeroError (extends \ArithmeticError)
+```
+
+<http://soba.tokyo.tequila.jp/developers/clemens/php/exceptions-tree.php>