Update label for plus code input to clarify its requirement for online events

Author: SableRaf

.github/ISSUE_TEMPLATE/new-event.yml

@@ -36,7 +36,7 @@ body:
   - type: input
     id: plus_code
     attributes:
-      label: Map placement (plus code)
+      label: Map placement (also required for online events)
       description: Find or verify the plus code for your event location at https://plus.codes.
       placeholder: 9F4MFCCM+JF
     validations: