fix: Use the recommended approach to add an attribute

docs/tutorial/PyMISP_tutorial.ipynb

@@ -216,7 +216,7 @@
     "del event.timestamp\n",
     "\n",
     "## Add the attribute to the event\n",
-    "event.attributes.append(attribute)\n",
+    "event.add_attribute(**attribute)\n",
     "\n",
     "## Push the updated event to MISP\n",
     "event_dict = misp.update(event)\n",