PyQt5 install needs to be forced after develop

Author: einarf

README.md

@@ -71,8 +71,8 @@ Installing the project in development mode (in a virtualenv):
 
 ```bash
 python setup.py develop
-# pyqt5 doesn't support develop and have to manually be installed after
-pip install PyQt5
+# PyQt5 doesn't support develop and have to manually be force-reinstalled installed after
+pip install -I PyQt5
 ```
 
 Running tests: