Update zenguard_library.ipynb

Author: Baur

docs/colabs/zenguard_library.ipynb

@@ -80,7 +80,9 @@
     {
       "cell_type": "markdown",
       "source": [
-        "### Configure API key:\n",
+        "## Prerequisites\n",
+        "\n",
+        "Configure an API key:\n",
         "1. Navigate to the [Settings](https://console.zenguard.ai/settings)\n",
         "2. Click on the **+ Create new secret key**.\n",
         "3. Name the key **Quickstart Key**.\n",