Update README.md

README.md

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 # PHP Dotenv
 
 Easy access to your environment variables set in the .env file.
+
+## INSTALLATION
+
+`composer require prinx/dotenv`
+
+## USAGE
+
+```php
+require_once __DIR__ . '/vendor/prinx/dotenv/Dotenv.php';
+
+use function Prinx\Dotenv\env;
+use function Prinx\Dotenv\set_env;
+
+// CURRENT_TOKEN will be accessible as environment the till the end of the script.
+set_env('CURRENT_TOKEN', 'rxLKo?LeP!FdGshvcxbs');
+
+// Throw an exception if DEV_DB_HOST does not exist in the .env
+$hostname = env('DEV_DB_HOST');
+
+// Will return 3306 if DEV_DB_PORT does not exist in the .env
+$port = env('DEV_DB_PORT', 3306);
+
+// May be in another file:
+$current_token = env('CURRENT_TOKEN');
+```
+
+Sample `.env` file:
+
+```env
+DEV_DB_HOST=dev_db_ip
+DEV_DB_PORT=3306
+
+PROD_DB_HOST=prod_db_ip
+PROD_DB_PORT=3308
+```
+
+### Getting an environment variable
+
+You need to put a the very top of the file the namespace of the function:
+
+```php
+// Top of the file
+use function Prinx\Dotenv\env;
+```
+
+There is two ways of getting the environment variables:
+
+#### 1. Using the `env()` function
+
+The simple way is to include the `Prinx\Dotenv\env` _function namespace_ at the top of the file and use the `env()` function anywhere in the file.
+
+```php
+// Top of the file
+use function Prinx\Dotenv\env;
+
+// Somewhere in the code
+$hostname = env('DEV_DB_HOST');
+```
+
+You can pass a default value that will be return if the variable is not found in the .env file:
+
+```php
+$hostname = env('DEV_DB_HOST', 'localhost');
+```
+
+### Setting an environment variable
+
+**Note:** Setting an environment variable using the library, will not save the variable inside your `.env` file. It will just make the variable accessible to you till the end of the script.
+
+You first need to put a the very top of the file the namespace of the function:
+
+```php
+// Top of the file
+use function Prinx\Dotenv\env;
+```
+
+There is two ways of setting the environment variables:
+
+#### 1. The simpler way: Using the `set_env()` function
+
+The simpler way is to include the `Prinx\Dotenv\set_env` _function namespace_ at the top of the file and use the `set_env()` function anywhere in the file.
+
+```php
+// Top of the file
+use function Prinx\Dotenv\set_env;
+
+// Somewhere in the code
+set_env('CURRENT_TOKEN', 'rxLKo?LeP!FdGshvcxbs');
+set_env('GUEST_NAME', 'john');
+```
+
+### The Dotenv class instance
+
+The recommended way to get or to set a variable has been seen above but you can also get or set a variable, using the Dotenv class instance:
+
+You access the `Dotenv` class instance by calling the `env()` function without any parameter:
+
+```php
+// Top of the file
+// No more need to use function Prinx\Dotenv\set_env; to be able to set a variable
+use function Prinx\Dotenv\env;
+```
+
+#### Getting a variable
+
+Then you use its `get()` static method to have access to the variables.
+
+```php
+$hostname = env()::get('DEV_DB_HOST');
+```
+
+With a default value:
+
+```php
+$hostname = env()::get('DEV_DB_HOST', 'localhost');
+```
+
+or
+
+```php
+$env = env();
+$hostname = $env::get('DEV_DB_HOST', 'localhost');
+```
+
+#### Setting a variable
+
+Use the `set()` static method to set a variable.
+
+```php
+env()::set('GUEST_NAME', 'john');
+```
+
+or
+
+```php
+$env = env();
+$env::set('GUEST_NAME', 'john');
+```