Update girder.ipynb

Author: claudioperez

docs/examples/girder.ipynb

@@ -4715,6 +4715,16 @@
    "cell_type": "markdown",
    "id": "e55b8771",
    "metadata": {},
+   "source": [
+    "## References \n",
+    "\n",
+    "- Paradiso, Massimo, Salvatore Sessa, Nicolò Vaiana, Francesco Marmo, and Luciano Rosati. “Shear Properties of Isotropic and Homogeneous Beam-like Solids Having Arbitrary Cross Sections.” International Journal of Solids and Structures 216 (May 2021): 231–49. https://doi.org/10.1016/j.ijsolstr.2021.01.012.\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ac1d2137",
+   "metadata": {},
    "source": []
   }
  ],