add donation links to GitHub FUNDING.yml

https://github.blog/2019-05-23-announcing-github-sponsors-a-new-way-to-contribute-to-open-source/

fdroiddata!5041
fdroidserver!668

[skip ci]
diff --git a/FUNDING.yml b/FUNDING.yml
new file mode 100644
index 0000000..75bb910
--- /dev/null
+++ b/FUNDING.yml
@@ -0,0 +1,8 @@
+---
+liberapay: F-Droid-Data
+github:
+    - eighthave
+custom:
+    - https://f-droid.org/about/
+    - https://www.hellotux.com/f-droid
+    - https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=E2FCXCT6837GL