Update contribute-to-avalanche notebook

notebooks/from-zero-to-hero-tutorial/09_contribute-to-avalanche.ipynb

@@ -9,7 +9,7 @@
     }
    },
    "source": [
-    "---\n",
+    "]---\n",
     "description: How to Contribute Back to the Avalanche Community\n",
     "---\n",
     "\n",
@@ -43,16 +43,19 @@
     "\n",
     "**The following rules should be respected:**\n",
     "\n",
-    "* Use PEP8 coding style and work within the 80 columns limit.\n",
+    "* Use [*Black*](https://github.com/psf/black) code formatting for a consistent coding style, which also handles line lengths (the 88 columns limit) automatically.\n",
     "* Always pull before pushing a commit.\n",
     "* Try to assign to yourself one issue at a time.\n",
     "* Try closing an issue **within roughly 7 days**. If you are not able to do that, please break it down into multiple ones you can tackle more easily, or you can always remove your assignment to the issue!\n",
     "* If you add a new feature, please include also a _test_ and a usage example in your PR.\n",
     "\n",
-    "Also, before making your PR **make sure** that the following commands return without any errors:\n",
+    "Also, before making your PR, first run the following command for code formatting with *Black*:\n",
+    "``` bash\n",
+    "black .\n",
+    "```\n",
     "\n",
+    "then, **make sure** that the following command returns no test errors:\n",
     "```bash\n",
-    "pycodestyle avalanche tests examples\n",
     "python -m unittest discover tests -v\n",
     "```\n",
     "\n",
@@ -86,6 +89,11 @@
     "You can run _this chapter_ and play with it on Google Colaboratory:\n",
     "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ContinualAI/avalanche/blob/master/notebooks/from-zero-to-hero-tutorial/09_contribute-to-avalanche.ipynb)"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": []
   }
  ],
  "metadata": {