Added README.md

Author: jon-fern

README.md

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+# Vapi PHP Library
+
+[![fern shield](https://img.shields.io/badge/%F0%9F%8C%BF-Built%20with%20Fern-brightgreen)](https://buildwithfern.com?utm_source=github&utm_medium=github&utm_campaign=readme&utm_source=https%3A%2F%2Fgithub.com%2FVapiAI%2Fserver-sdk-php)
+[![php shield](https://img.shields.io/badge/php-packagist-pink)](https://packagist.org/packages/vapi/vapi)
+
+The Vapi PHP library provides convenient access to the Vapi API from PHP.
+
+## Requirements
+
+This SDK requires PHP ^8.1.
+
+## Installation
+
+```sh
+composer require vapi/vapi
+```
+
+## Usage
+
+Instantiate and use the client with the following:
+
+```php
+<?php
+
+use Vapi\VapiClient;
+use Vapi\Calls\Requests\CreateCallDto;
+
+$client = new VapiClient(token: '<YOUR_TOKEN>');
+
+$call = $client->calls->create(
+    new CreateCallDto([
+        'name' => 'My Call',
+        'assistantId' => 'your-assistant-id',
+    ])
+);
+```
+
+## Exception Handling
+
+When the API returns a non-success status code (4xx or 5xx response), an exception will be thrown.
+
+```php
+use Vapi\Exceptions\VapiApiException;
+use Vapi\Exceptions\VapiException;
+
+try {
+    $call = $client->calls->create(...);
+} catch (VapiApiException $e) {
+    echo 'API Exception occurred: ' . $e->getMessage() . "\n";
+    echo 'Status Code: ' . $e->getCode() . "\n";
+    echo 'Response Body: ' . $e->getBody() . "\n";
+}
+```
+
+## Advanced
+
+### Custom Client
+
+This SDK is built to work with any HTTP client that implements Guzzle's `ClientInterface`.
+By default, if no client is provided, the SDK will use Guzzle's default HTTP client.
+However, you can pass your own client that adheres to `ClientInterface`:
+
+```php
+use Vapi\VapiClient;
+
+// Create a custom Guzzle client with specific configuration.
+$customClient = new \GuzzleHttp\Client([
+    'timeout' => 5.0,
+]);
+
+// Pass the custom client when creating an instance of the class.
+$client = new VapiClient(
+    token: '<YOUR_TOKEN>',
+    options: [
+        'client' => $customClient
+    ]
+);
+
+// You can also utilize the same technique to leverage advanced customizations to the client such as adding middleware
+$handlerStack = \GuzzleHttp\HandlerStack::create();
+$handlerStack->push(MyCustomMiddleware::create());
+$customClient = new \GuzzleHttp\Client(['handler' => $handlerStack]);
+
+// Pass the custom client when creating an instance of the class.
+$client = new VapiClient(
+    token: '<YOUR_TOKEN>',
+    options: [
+        'client' => $customClient
+    ]
+);
+```
+
+### Retries
+
+The SDK is instrumented with automatic retries with exponential backoff. A request will be retried as long
+as the request is deemed retryable and the number of retry attempts has not grown larger than the configured
+retry limit (default: 2).
+
+A request is deemed retryable when any of the following HTTP status codes is returned:
+
+- [408](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/408) (Timeout)
+- [429](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/429) (Too Many Requests)
+- [5XX](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/500) (Internal Server Errors)
+
+Use the `maxRetries` request option to configure this behavior.
+
+```php
+$call = $client->calls->create(
+    new CreateCallDto([...]),
+    options: [
+        'maxRetries' => 0 // Override maxRetries at the request level
+    ]
+);
+```
+
+### Timeouts
+
+Use the `timeout` option to configure request timeouts.
+
+```php
+$call = $client->calls->create(
+    new CreateCallDto([...]),
+    options: [
+        'timeout' => 3.0 // Override timeout to 3 seconds
+    ]
+);
+```
+
+## Contributing
+
+While we value open-source contributions to this SDK, this library is generated programmatically.
+Additions made directly to this library would have to be moved over to our generation code,
+otherwise they would be overwritten upon the next generated release. Feel free to open a PR as
+a proof of concept, but know that we will not be able to merge it as-is. We suggest opening
+an issue first to discuss with us!
+
+On the other hand, contributions to the README are always very welcome!
+