Update sponsoring info

.github/FUNDING.yml

@@ -0,0 +1,2 @@
+github: svoop
+custom: "https://donorbox.org/bitcetera"

README.md

@@ -1,7 +1,7 @@
 [![Version](https://img.shields.io/gem/v/notam.svg?style=flat)](https://rubygems.org/gems/notam)
 [![Tests](https://img.shields.io/github/actions/workflow/status/svoop/notam/test.yml?style=flat&label=tests)](https://github.com/svoop/notam/actions?workflow=Test)
 [![Code Climate](https://img.shields.io/codeclimate/maintainability/svoop/notam.svg?style=flat)](https://codeclimate.com/github/svoop/notam/)
-[![Donorbox](https://img.shields.io/badge/donate-on_donorbox-yellow.svg)](https://donorbox.org/bitcetera)
+[![GitHub Sponsors](https://img.shields.io/github/sponsors/svoop.svg)](https://github.com/sponsors/svoop)
 
 # NOTAM
 
@@ -11,6 +11,8 @@ Parser for [NOTAM (Notice to Air Missions)](https://www.icao.int/safety/istars/p
 * [API](https://www.rubydoc.info/gems/notam)
 * Author: [Sven Schwyn - Bitcetera](https://bitcetera.com)
 
+Thank you for supporting free and open-source software by sponsoring on [GitHub](https://github.com/sponsors/svoop) or on [Donorbox](https://donorbox.com/bitcetera). Any gesture is appreciated, from a single Euro for a ☕️ cup of coffee to 🍹early retirement.
+
 ## Install
 
 ### Security