add readme for testing php embed

examples/readme.md

+# To test php example
+
+(1) 
+
+Start PHP webserver
+
+```txt
+$ cd examples
+$ php -S localhost:9000
+[Fri Mar  7 09:01:52 2025] PHP 8.4.4 Development Server (http://localhost:9000) started
+```
+
+(2)
+
+In a webbrowser open <http://localhost:9000/embed_example.php>