feat: php-spx documentation

Author: SamJUK

configuration/phpspx.md

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+# PHP SPX Profiling
+
+PHP SPX is a simple, free and open source profiler. It covers both FPM and CLI requests, and provides a built-in UI to visualise the generated reports. Of which a [demo can be seen here](https://noisebynorthwest.github.io/php-spx/demo/report.html?key=spx-full-20191229_175636-06d2fe5ee423-3795-233665123).
+
+For more information, please see the [PHP SPX Github Repository](https://github.com/NoiseByNorthwest/php-spx).
+
+
+## Configuration
+
+
+To enable PHP SPX in your project environment, add to your `.env` file:
+```
+WARDEN_PHP_SPX=1
+```
+
+## Usage
+
+### CLI
+
+Running the `warden spx` command, will place you within a PHP-SPX instrumented terminal. Where any PHP commands you run will be profiled.
+
+You should see a SPX report printed after the command finishes. And there will also be a corresponding report within the control panel.
+
+![Example CLI Report generated with PHP SPX](screenshots/phpspx-cli-report.png)
+
+
+### Web
+
+Once an environment is started with the `WARDEN_PHP_SPX=1` flag set, all web requests will be profiled. To override this, you can uncheck the `Automatic start` option within the control panel. 
+
+![Example Web Report generated with PHP SPX](screenshots/phpspx-web-report.png)
+
+### Control Panel / Viewer
+
+To view the reports generated by PHP SPX, append `?SPX_UI_URI=/` to the end of your environment url (e.g `https://app.magento2.test/?SPX_UI_URI=/`). 
+
+![Example PHP SPX Control Panel](screenshots/phpspx-control-panel.png)