PHP Quickstart: config and autoloading (follow-up to @xepozz's #4151) (#4166)

* feat: introduce PHP quickstart guide

* Alphabetized quickstarts order

* edits to set up flow and config steps

* spelling + grammar

* more edits

* format

---------

Co-authored-by: Dmitriy Derepko <xepozz@list.ru>

Author: jsundai

docs/develop/php/index.mdx

@@ -20,6 +20,7 @@ Build Temporal Applications with the PHP SDK.
 
 **Temporal PHP Technical Resources:**
 
+- [PHP SDK Quickstart - Setup Guide](/develop/php/set-up-your-local-php)
 - [PHP API Documentation](https://php.temporal.io)
 - [PHP SDK Code Samples](https://github.com/temporalio/samples-php)
 - [PHP SDK GitHub](https://github.com/temporalio/sdk-php)