Added the python version requirement to the README.

README.md

@@ -3,6 +3,7 @@ Swift Website
 
 This is the website for the SWIFT project. You can build the website by doing the following:
 
++ Have python 3.6 or more recent and pip 3.6.
 + Create a virtual environment (`` virtualenv3 env `` or `` virtualenv env``) and ensure that it is `` python3 ``.
 + Activate it (`` source env/bin/activate ``) [note to deactivate you want to use the `` deactivate `` keyword in your shell]
 + Use that virtual environment to install the required packages (`` pip install -r requirements.txt ``)