Readme: Use Fully Qualified Class Names for examples

So that developers can more easily copy and paste the entire code snippet and use it in their applications.

Also adds type hinting for the $response model type.

README.md

@@ -17,10 +17,11 @@ Integrating OpenAI into your application is now as simple as a few lines of code
 ### Text Completion using GPT-3
 
 ```php
-$openaiClient = Manager::build(new \GuzzleHttp\Client(), new Authentication(getenv('OPENAI_API_KEY')));
+$openaiClient = \Tectalic\OpenAi\Manager::build(new \GuzzleHttp\Client(), new \Tectalic\OpenAi\Authentication(getenv('OPENAI_API_KEY')));
 
+/** @var \Tectalic\OpenAi\Models\Completions\CreateResponse $response */
 $response = $openaiClient->completions()->create(
-    new CreateRequest([
+    new \Tectalic\OpenAi\Models\Completions\CreateRequest([
         'model'  => 'text-davinci-002',
         'prompt' => 'Will using a third party package save time?',
     ])
@@ -35,10 +36,11 @@ echo $response->choices[0]->text;
 ### Code Completion Using Codex
 
 ```php
-$openaiClient = Manager::build(new \GuzzleHttp\Client(), new Authentication(getenv('OPENAI_API_KEY')));
+$openaiClient = \Tectalic\OpenAi\Manager::build(new \GuzzleHttp\Client(), new \Tectalic\OpenAi\Authentication(getenv('OPENAI_API_KEY')));
 
+/** @var \Tectalic\OpenAi\Models\Completions\CreateResponse $response */
 $response = $openaiClient->completions()->create(
-    new CreateRequest([
+    new \Tectalic\OpenAi\Models\Completions\CreateRequest([
         'model'  => 'code-davinci-002',
         'prompt' => "// PHP 8\n// A variable that saves the current date and time",
         'max_tokens' => 256,
@@ -55,10 +57,11 @@ echo $response->choices[0]->text;
 ### Image Generation Using DALL·E
 
 ```php
-$openaiClient = Manager::build(new \GuzzleHttp\Client(), new Authentication(getenv('OPENAI_API_KEY')));
+$openaiClient = \Tectalic\OpenAi\Manager::build(new \GuzzleHttp\Client(), new \Tectalic\OpenAi\Authentication(getenv('OPENAI_API_KEY')));
 
+/** @var \Tectalic\OpenAi\Models\ImagesGenerations\CreateResponse $response */
 $response = $openaiClient->imagesGenerations()->create(
-    new CreateRequest([
+    new \Tectalic\OpenAi\Models\ImagesGenerations\CreateRequest([
         'prompt' => 'A cute baby sea otter wearing a hat',
         'size' => '256x256',
         'n' => 5