update python on virtualenv code example

Example 1: python virtual environment

python3 -m venv env
python -m virtualenv env #py2

source env/bin/activate

#all this is on same directory

Example 2: how to use virtual environment python

python3 -m pip install --user virtualenv

Example 3: python virtual env

$ virtualenv -p /usr/bin/python2.7 venv

Example 4: how to activate the pytho virtual environment

mypthon\Scripts\activate