Add PHP example for using the HTTP daemon in docs. (#61)

* Add PHP example for using the HTTP daemon in docs.

* Use procedural code for example snippet

* Remove this variable

docs/daemon.md

@@ -86,6 +86,22 @@ fetch("http://localhost:8080", requestOptions)
   .then(result => console.log(result))
   .catch(error => console.log('error', error));
 ```
+
+* `PHP` (Symfony HttpClient)
+```php
+$httpClient = HttpClient::create();
+
+$response = $httpClient->request('POST', 'http://localhost:8080', [
+  'headers' => [
+    'Content-Type' => 'application/xml',
+  ],
+  'body' => fopen('/path/to/some.xml', 'r'),
+]);
+
+echo $response->getContent();
+
+```
+
 ## Status codes
 | code | description |
 |-|-|