update issue template for instances

.gitea/ISSUE_TEMPLATE/instance.yml

@@ -48,4 +48,7 @@ body:
       label: Contact details
       description: Input your contact information should we need to contact you privately. We recommend Matrix. If you don't have a contact method, or don't want your contact method public, tell us.
       placeholder: "@foo:example.org"
-      
+  - type: checkboxes
+    attributes:
+      label: Instance Rules
+      description: I have read and accepted the [instance rules](https://codeberg.org/gothub/gothub#instance-rules)