Colab tutorials (#367)

* Colab Button & Run added

tutorials/tutorial7/tutorial.ipynb

@@ -5,7 +5,9 @@
    "id": "dbbb73cb-a632-4056-bbca-b483b2ad5f9c",
    "metadata": {},
    "source": [
-    "# Tutorial: Resolution of an inverse problem"
+    "# Tutorial: Resolution of an inverse problem\n",
+    "\n",
+    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/mathLab/PINA/blob/master/tutorials/tutorial7/tutorial.ipynb)"
    ]
   },
   {
@@ -53,6 +55,15 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "## routine needed to run the notebook on Google Colab\n",
+    "try:\n",
+    "  import google.colab\n",
+    "  IN_COLAB = True\n",
+    "except:\n",
+    "  IN_COLAB = False\n",
+    "if IN_COLAB:\n",
+    "  !pip install \"pina-mathlab\"\n",
+    "  \n",
     "import matplotlib.pyplot as plt\n",
     "import torch\n",
     "from pytorch_lightning.callbacks import Callback\n",