update broken link

README.md

@@ -81,7 +81,7 @@ The images in the paper are sometime small.  We offer high resolution images to
 
 ## Code
 
-The images above have been generated using code from the [Code folder](./Code/)
+The images above have been generated using code from the [Code folder](./code)
 It is mainly code to preprocess the data files that will then be processed in d3.js.
 The exemples of visualisations are accessible online at the following adresses (checked on the <span class="timestamp-wrapper"><span class="timestamp">&lt;2019-05-22 mer.&gt;</span></span>):
 
@@ -104,9 +104,9 @@ Visualizations on <https://observablehq.com/@maliky/playing-with-moodle-data>
 
 ### Coursera
 
-Use the file <Code/SNA-Coursera17/> folder to scrap the data from a Coursera and then wrangle it into visualisation.
+Use the [folder](./Code/SNA-Coursera17/) to scrap the data from a Coursera and then wrangle it into visualisation.
 
 -   The visualisation requires `graph_tool.py`
 
-Check the <Code/SNA-Coursera17/README.md> 
+Check the [README.md in Code/SNA-Coursera17](./Code/SNA-Coursera17/README.md)