use python as python3 zsh code example

Example 1: mac why is python installed in usr and application

$ pyenv global 3.7.3
# and verify it worked 
$ pyenv version
3.7.3 (set by /Users/mbbroberg/.pyenv/version)

Example 2: use python as python3 zsh

# Go into your .zshrc file. Is there a line that reads:
alias python='python3'