feat: php-spx documentation

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
+```
+
+:::{note}
+When disabling SPX, you may be presented with a 502 bad gateway when the environment is next restarted, or the SPX container is removed.
+
+This is caused due to the SPX cookies still being set in your browser. There is a helper tool to aid in removing these on the 502 page, or you can remove them manually through developer tools.
+:::
+
+## 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` the SPX control panel will be available. 
+
+You can start profiling requests, either by enabling the `Enabled` checkbox within the Control Panel. Or by setting the `SPX_ENABLED` browser cookie to a value of `1`
+
+![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=/&SPX_KEY=warden` to the end of your environment url (e.g `https://app.magento2.test/?SPX_UI_URI=/&SPX_KEY=warden`). 
+
+![Example PHP SPX Control Panel](screenshots/phpspx-control-panel.png)
+
+## Troubleshooting
+
+### Control Panel not accessible
+
+1. Check that `WARDEN_PHP_SPX=1` is enabled within your `.env` file
+2. Check that the SPX container is running `warden env ps php-spx`
+3. Make sure you specify the `SPX_KEY` query parameter with the value of `warden` when visiting the dashboard for the first time.
+4. Make sure you do not have XDebug cookies or arguments set. The Debug container takes priority over SPX.
+5. Check the `x-backend` response header, to ensure the request is correctly being routed to the SPX container.
+
+### 502 Bad Gateway when disabling SPX
+
+This is expected behavior when disabling SPX, as it does not automatically clean your cookies.
+
+The 502 bad gateway page, has a helper tool that will help you clear the relevant SPX cookies.
+Or you can manually remove these from within dev tools, and refresh the page.