Other doc fixes

README.md

@@ -17,7 +17,8 @@ Python 3.
 $ sudo apt-get update
 $ sudo apt-get install git pip python-setuptools
 ```
-Make sure you got Python 3:
+**N.B.** Python 3 is now the default interpreter in most recent Linux
+distributions. Do not use Python 2! If unsure, check with:
 ```shell
 $ python -V
 ```