[docs] Fix model path in IR getting started (#1604)

Fixes #1600 by using a
relative path. Validated with sphinx.

docs/intermediate_representation/getting_started.ipynb

@@ -18,19 +18,12 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "import pathlib\n",
-    "\n",
     "import onnx\n",
     "\n",
     "from onnxscript import ir\n",
     "\n",
     "# Load the model as onnx.ModelProto\n",
-    "model_proto = onnx.load(\n",
-    "    pathlib.Path(ir.__file__).parent.parent.parent\n",
-    "    / \"testdata\"\n",
-    "    / \"dort_models\"\n",
-    "    / \"llama_forward.onnx\"\n",
-    ")\n",
+    "model_proto = onnx.load(\"../../testdata/dort_models/llama_forward.onnx\")\n",
     "\n",
     "# Create an IR object from the model\n",
     "model = ir.serde.deserialize_model(model_proto)"
@@ -1479,7 +1472,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.9"
+   "version": "3.11.9"
   }
  },
  "nbformat": 4,