Add JetBrains sponsorship to README with H1 heading (#37)

Author: g105b

README.md

@@ -47,3 +47,9 @@ $loop->addTimer($timer);
 echo "Starting...", PHP_EOL;
 $loop->run();
 ```
+
+# Proudly sponsored by
+
+[JetBrains Open Source sponsorship program](https://www.jetbrains.com/community/opensource/)
+
+[![JetBrains logo.](https://resources.jetbrains.com/storage/products/company/brand/logos/jetbrains.svg)](https://www.jetbrains.com/community/opensource/)