Add PayPal to FUNDING

Author: purejava

.github/FUNDING.yml

@@ -10,4 +10,4 @@ liberapay: # Replace with a single Liberapay username
 issuehunt: # Replace with a single IssueHunt username
 otechie: # Replace with a single Otechie username
 lfx_crowdfunding: # Replace with a single LFX Crowdfunding project-name e.g., cloud-foundry
-custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
+custom: ['https://www.paypal.com/donate?hosted_button_id=XVX9ZM7WE4ANL']