update python venv 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: create a virtualenv python

pip install virtualenv
cd projectfolder #go to project folder
virtualenv projectname #create the folder projectname 
source projectname/bin/activate

Example 3: venv upgrade python

python3 -m venv --upgrade ENV_DIR