Update README

Author: davistdaniel

README.md

@@ -15,7 +15,7 @@ The library is born out of a collection of scripts I wrote for routine analysis
 
 Run in a terminal : 
 
-`python -m pip install -i https://test.pypi.org/simple/ eprpy`
+`pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple eprpy`
 
 ### From source
 Clone the [EPRpy repository](https://davistdaniel.github.io/EPRpy/) and then navigate to the folder where setup.py file is present.