Note about different python installations.

Author: gannimo

README.md

@@ -50,7 +50,7 @@ and then issues a warning.
 You can run the DP3T reference implementation with your favorite `python3`
 interpreter. The only additional package you need is `Cryptodome`. You can
 install it, e.g., through `sudo apt install python3-pycryptodome` or
-`pip install pycryptodome`.
+`pip3 install pycryptodome` (or `pip` if you only have python3 installed).
 
 
 ## Example run