Fix: Add opening tags and strict declaration to examples

README.md

@@ -26,6 +26,10 @@ $ composer require ergebnis/environment-variables
 If you want to read, set, and unset environment variables in an object-oriented way in a production environment, you can use [`Ergebnis\Environment\Variables\Production`](src/Production.php):
 
 ```php
+<?php
+
+declare(strict_types=1);
+
 use Ergebnis\Environment\Variables;
 
 final class BuildEnvironment
@@ -61,6 +65,10 @@ If your tests depend on environment variables, you have the following challenges
 To solve this problem, you can use [`Ergebnis\Environment\Variables\Test`](src/Test.php):
 
 ```php
+<?php
+
+declare(strict_types=1);
+
 use Ergebnis\Environment\Variables;
 use PHPUnit\Framework;