run nmp install before npm start in readme.md

[wi-wi]

run
nmp install
before
npm start
in readme.md

[bogdanudrescu]

Hi, for consistency this should be an easy fix to add npm install command. Besides this I wasn't able to run it at first, needed to update the react version before running npm install.

Thank you for this demo @WebDevSimplified, I appreciate it, it was really helpful!