Remove suggestion to use sudo in favor of Python virtual environments

[carlthome]

IIRC as of Python 3.3, there's built-in support for creating a virtual environments.

So since Python 2 has now reached EOL, beginner users in MIR can be discouraged from running sudo pip install (as that can break their system).

As a suggestion: the README could mention using the now included venv package instead.

[urinieto]

Looking good, thanks!