feat: added GreaterThan rule documentation

Author: andrepimpao

docs/03-rules-greater-than.md

@@ -0,0 +1,41 @@
+# GreaterThan
+
+Validates that a value is greater than another value. Can compare between strings, numbers and dates.
+
+## Basic Usage
+
+```php
+Validator::greaterThan(10)->validate(20); // true
+Validator::greaterThan(1.5)->validate(2.5); // true
+Validator::greaterThan('alpha')->validate('beta'); // true
+Validator::greaterThan(new DateTime('today'))->validate(new DateTime('tomorrow')); // true
+```
+
+> **Note**
+> String comparison is case-sensitive, meaning that comparing `'hello'` with `'Hello'` is different. 
+> Check [`strcmp`](https://www.php.net/manual/en/function.strcmp.php) for more information.
+
+> **Note**
+> An `UnexpectedValueException` will be thrown when trying to compare incomparable values, like a `string` with an `int`.
+
+## Options
+
+### `constraint`
+
+type: `mixed` `required`
+
+It defines the comparison/minimum value. Can be a string, number or `DateTimeInterface` object.
+
+### `message`
+
+type: `string` default: `The "{{ name }}" value should be greater than "{{ constraint }}", "{{ value }}" given.`
+
+Message that will be shown if the value is not greater than the constraint value. Check the [Custom Messages]() section for more information.
+
+The following parameters are available:
+
+| Parameter          | Description                        |
+|--------------------|------------------------------------|
+| `{{ value }}`      | The current invalid value          |
+| `{{ name }}`       | Name of the value being validated  |
+| `{{ constraint }}` | The comparison/minimum value       |