Add npm and yarn version requirements needed to setup a local copy

Author: lukekarrys

CONTRIBUTING.md

@@ -90,6 +90,8 @@ All functionality must be retained (and configuration given to the user) if they
 
 ## Setting Up a Local Copy
 
+You will need `npm@7` and `yarn@1` in order to bootstrap and test a local copy of this repo.
+
 1. Clone the repo with `git clone https://github.com/facebook/create-react-app`
 
 2. Run `npm install` in the root `create-react-app` folder.