Added the link to the legacy validator

Author: melanieganz

PETBIDS-Onboarding2025/BIDS_conversion_tutorial_Colab.ipynb

@@ -723,12 +723,31 @@
     "!tree ./OpenNeuroPET-Phantoms/ --filelimit 15"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Now let's see if the dataset is valid...."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Online validation\n",
+    "\n",
+    "Go to https://bids-standard.github.io/legacy-validator/ and select the folder `OpenNeuroPET-Phantoms` to see if it is valid.\n",
+    "(Note we are using the legacy validator since the other one has a runtime issue right now.)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {
     "id": "mrqQYEMWNHPJ"
    },
    "source": [
+    "## More advanced BIDS conversion\n",
+    "\n",
     "So even though there are libraries that do part of the BIDS conversion for you, there is often some manual work to be done wrt file renaming or adding additional files on top.\n",
     "\n",
     "Converters like EZBids or BIDScoin try to even alleviate this burden.\n",