Update README.md

Author: AustL

README.md

@@ -1,5 +1,7 @@
 # PySolarCell
 
+![](https://img.shields.io/pypi/dm/pysolarcell)
+
 A detailed balance solar cell solver for multijunction tandem solar cells. It supports IV and EQE calculation, and different connection types between layers e.g. series, parallel and mixed.
 
 ## Installation
@@ -12,4 +14,4 @@ Open a Python console and run the following command.
 
 ```import pysolarcell```
 
-If you receive no errors, the installation was successful.
+If you receive no errors, the installation was successful.