Update FUNDING.yml

add NumFOCUS github sponsors button (recurring donations only)

This feature is launching today at GitHub Universe!

Also updated the custom link to point directly to the PyMC3 designated donations form.

cc @fonnesbeck

Author: Dr-G

.github/FUNDING.yml

@@ -1,6 +1,6 @@
 # These are supported funding model platforms
 
-github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+github: numfocus
 patreon: # Replace with a single Patreon username
 open_collective: # Replace with a single Open Collective username
 ko_fi: # Replace with a single Ko-fi username
@@ -9,4 +9,4 @@ community_bridge: # Replace with a single Community Bridge project-name e.g., cl
 liberapay: # Replace with a single Liberapay username
 issuehunt: # Replace with a single IssueHunt username
 otechie: # Replace with a single Otechie username
-custom: ['https://numfocus.org/donate'] # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
+custom: ['https://numfocus.org/donate-to-pymc3'] # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']