add Module1_Unit4 reference content

Module_1/Module1_Unit4.ipynb

@@ -151,7 +151,9 @@
   {
    "cell_type": "markdown",
    "id": "5ef35a39-2bbb-4d95-9d6c-d7cca0740047",
-   "metadata": {},
+   "metadata": {
+    "tags": []
+   },
    "source": [
     "Here are some other examples of data science questions we could explore with students as part of our regular curriculum:\n",
     "\n",
@@ -177,7 +179,20 @@
     "\n",
     "### Conclusion \n",
     "\n",
-    "In this module, we have introduced data science and how it relates to education. The next module will have us using data, and will introduce Jupyter notebooks."
+    "In this module, we have introduced data science and how it relates to education. The next module will have us using data, and will introduce Jupyter notebooks.\n",
+    "\n",
+    "### References \n",
+    "\n",
+    "Reference materials\n",
+    "* A web comic featuring math and programming humour - [XKCD](https://xkcd.com/).\n",
+    "* The importance of digital and data literacy - [National Skills Coalition.](https://medium.com/national-skills-coalition/digital-fluency-for-a-resilient-economy-38bf4a9e569c)\n",
+    "* High school data science education, a student perspective - [Harvard Data Science Review.](https://hdsr.mitpress.mit.edu/pub/wtzfot43/release/2)\n",
+    "* Key data science concepts:\n",
+    "    * [https://simple.wikipedia.org/wiki/Data_science](https://simple.wikipedia.org/wiki/Data_science)\n",
+    "    * [en.wikipedia.org/wiki/Data_cleansing](https://en.wikipedia.org/wiki/Data_cleansing)\n",
+    "    * [en.wikipedia.org/wiki/Tidy_data](https://en.wikipedia.org/wiki/Tidy_data)\n",
+    "    * [en.wikipedia.org/wiki/Data_visualization](https://en.wikipedia.org/wiki/Data_visualization)\n",
+    "    * [en.wikipedia.org/wiki/Literate_programming](https://en.wikipedia.org/wiki/Literate_programming)"
    ]
   },
   {