Add JetBrains sponsorship to README with H1 heading (#64)

Author: g105b

README.md

@@ -43,3 +43,9 @@ $lookup = function()use($ipAddress):string {
 $location = $fileCache->get("lat-lon", $lookup);
 echo "Your location is: $location";
 ```
+
+# 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/)