Update Readme.md

Author: dewelobya

DataVisualization/Readme.md

@@ -2,11 +2,11 @@
 
 **D3, APIs, and AJAX**
 
-1. [Visualize Data with a Bar Chart]()
-2. [Visualize Data with a Scatterplot Graph]()
-3. [Visualize Data with a Heat Map]()
-4. [Visualize Data with a Choropleth Map]()
-5. [Visualize Data with a Treemap Diagram]() 
+1. [Visualize Data with a Bar Chart](https://codepen.io/peill/pen/XWyNbbq)
+2. [Visualize Data with a Scatterplot Graph](https://codepen.io/peill/pen/OJaBraW)
+3. [Visualize Data with a Heat Map](https://codepen.io/peill/pen/BaGqvvW)
+4. [Visualize Data with a Choropleth](https://codepen.io/peill/pen/RwqeEda)
+5. [Visualize Data with a Treemap Diagram](https://codepen.io/pen?template=MJjpwO)