Add: documentation about updating contributor names in the contributors.yml file only

[lwasser]

Update the README file in this repo to explain that:

you can update a contributors name as it appears on our website here by updating their name in the _data/contributors.yml file.

If someone tries to update it in the _data/packages.yml file with the name it will be overwritten.

This is because our workflow treats the contributors.yml file as the singel source of truth and the single plae to manage people. The names listed here assume that we can gather metadata based on a contributor's GitHub username from the contributor file.