add references

semicustom/semicustom-inverter.ipynb

@@ -198,6 +198,15 @@
     "print(f\"cvc_total_errors        {metrics['cvc_total_errors'][0]}\")\n",
     "print(f\"klayout_violations      {metrics['klayout_violations'][0]}\")"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# References\n",
+    "Inspired from:\n",
+    "“Silicon Notebooks.” CHIPS Alliance, Apr. 08, 2023. Accessed: Apr. 10, 2023. [Online]. Available: https://github.com/chipsalliance/silicon-notebooks/blob/b65134a43b01ae31423f7ee87110740b2257ac42/digital-inverter-openlane.ipynb (Apache License 2.0)"
+   ]
   }
  ],
  "metadata": {
@@ -220,7 +229,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.16"
+   "version": "3.10.9"
   }
  },
  "nbformat": 4,