Merge pull request #543 from jamiehannaford/working

Adding explanation for prefixing user-agents

Author: ycombinator

docs/userguide/Clients.md

@@ -116,6 +116,34 @@ To set default HTTP headers:
 $client->setDefaultOption('headers/X-Custom-Header', 'FooBar');
 ```
 
+## User agents
+
+php-opencloud will send a default `User-Agent` header for every HTTP request, unless a custom value is provided by the end-user. The default header will be in this format:
+
+> User-Agent: OpenCloud/xxx cURL/yyy PHP/zzz
+
+where `xxx` is the current version of the SDK, `yyy` is the current version of cURL, and `zzz` is the current PHP version. To override this default, you must run:
+
+```php
+$client->setUserAgent('MyCustomUserAgent');
+```
+
+which will result in:
+
+> User-Agent: MyCustomUserAgent
+
+If you want to set a _prefix_ for the user agent, but retain the default `User-Agent` as a suffix, you must run:
+
+```php
+$client->setUserAgent('MyPrefix', true);
+```
+
+which will result in:
+
+> User-Agent: MyPrefix OpenCloud/xxx cURL/yyy PHP/zzz
+
+where `$client` is an instance of `OpenCloud\OpenStack` or `OpenCloud\Rackspace`.
+
 ## 5. Other functionality
 
 For a full list of functionality provided by Guzzle, please consult the [official documentation](http://docs.guzzlephp.org/en/latest/http-client/client.html).