update to git code example

Example 1: how to update your local repository

First, navigate to the desired directory:

$ cd ~/Documents/GitHub/DI-NEON-participants

And then type:

$ git remote add upstream https://github.com/NEONS...

Update local repo using git pull with the added directions of 
upstream indicating the central repository and master specifying 
which branch you are pulling down:

$ git pull upstream master

Example 2: how to update local repo when i make changes to github remote repo

git pull origin master_or_other_branch_name