Create FUNDING.yml

Added the osgeo sponsorship option, and links to our sponsorship details.

The external links are displayed as-is - so the PayPal link looks terrible...

Author: jodygarnett

.github/FUNDING.yml

@@ -0,0 +1,4 @@
+# These are supported funding model platforms
+
+github: [osgeo]
+custom: ['https://github.com/geoserver/geoserver/wiki/Sponsor','https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=4XZ76BZMEWZ24&source=url']