I agree with Martin that this belongs in the input() rather than readline() docs. However, the input() does is quite concise, and the sole example specifies the right way to use it:

https://docs.python.org/3/library/functions.html#input

I find it hard to justify real estate in this doc in which to explain what happens if you combine input with readline and do the wrong thing. 

I suggest we leave it as it is.