include FUNDING.yml directly, `fdroid update` reads it

Also, it is the number two hit when searching for "FUNDING.yml":
https://duckduckgo.com/html/?q=funding.yml

This was copied from https://github.com/f-droid/.github.git

FUNDING.yml

@@ -0,0 +1,11 @@
+---
+liberapay: F-Droid-Data
+open_collective: F-Droid
+github:
+    - f-droid
+    - eighthave
+custom:
+    - https://f-droid.org/donate/
+    - https://www.hellotux.com/f-droid
+    - https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=E2FCXCT6837GL
+    - https://blockchain.info/address/15u8aAPK4jJ5N8wpWJ5gutAyyeHtKX5i18