Add axelrod to project.

- Include logo
- Include md

We have not decided on version number for dropping py2 support but we
will be dropping it on the 1st of December.

Author: drvinceknight

_sections/30-projects.md

@@ -20,6 +20,7 @@ style: center
 - [![](assets/pystan.png)PyStan](https://github.com/stan-dev/pystan)
 - [![](assets/osbrain.png)osBrain](https://github.com/opensistemas-hub/osbrain)
 - [![](assets/pymeasure.png)PyMeasure](https://github.com/ralph-group/pymeasure)
+- [![](assets/axelrod.png)Axelrod](https://github.com/Axelrod-Python/Axelrod)
 
 &nbsp; <!--break separating project with image from without -->