Add "extra infos" field to issue template

.github/ISSUE_TEMPLATE/new_instance.yaml

@@ -76,3 +76,12 @@ body:
         required: false
       - label: "You have provided the source code's URL in the dedicated field above"
         required: false
+
+  - type: textarea
+    id: more-infos
+    attributes:
+      label: Additionnal informations
+      description: "If your want to add other informations on your instance, do so here:"
+      placeholder: "Example: Our instance also has an .onion URL, The source code changes are ..., etc."
+    validations:
+      required: false