[Dotenv] improve documentation for dotenv component

README.md

@@ -11,6 +11,15 @@ Getting Started
 composer require symfony/dotenv
 ```
 
+Usage
+-----
+
+> For an .env file with this format:
+
+```env
+YOUR_VARIABLE_NAME=my-string
+```
+
 ```php
 use Symfony\Component\Dotenv\Dotenv;
 
@@ -25,6 +34,12 @@ $dotenv->overload(__DIR__.'/.env');
 
 // loads .env, .env.local, and .env.$APP_ENV.local or .env.$APP_ENV
 $dotenv->loadEnv(__DIR__.'/.env');
+
+// Usage with $_ENV
+$envVariable = $_ENV['YOUR_VARIABLE_NAME'];
+
+// Usage with $_SERVER
+$envVariable = $_SERVER['YOUR_VARIABLE_NAME'];
 ```
 
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