[Nominatim] Update Readme.md

Related to #1061

Author: jbelien

src/Provider/Nominatim/Readme.md

@@ -12,13 +12,27 @@ This is the Nominatim provider from the PHP Geocoder. This is a **READ ONLY** re
 
 All usage of the Nominatim provider using `nominatim.openstreetmap.org` must follow the [Nominatim Usage Policy](https://operations.osmfoundation.org/policies/nominatim/) !
 
-### Install
+## Install
 
 ```bash
 composer require geocoder-php/nominatim-provider
 ```
 
-### Contribute
+## Usage
+
+If you want to use the "default" Nominatim instance (https://nominatim.openstreetmap.org/) :
+
+```php
+$provider = \Geocoder\Provider\Nominatim::withOpenStreetMapServer($httpClient, $userAgent);
+```
+
+If you want to specify yourself the server that will be used :
+
+```php
+$provider = new \Geocoder\Provider\Nominatim($httpClient, 'https://nominatim.openstreetmap.org', $userAgent);
+```
+
+## Contribute
 
 Contributions are very welcome! Send a pull request to the [main repository](https://github.com/geocoder-php/Geocoder) or 
 report any issues you find on the [issue tracker](https://github.com/geocoder-php/Geocoder/issues).