Update README for Angular 14

The README makes reference to Angular 13 being required, but it is now Angular 14 that is required.

An alternative would be to say something along the lines of "check package.json to see which Angular version to use," but I believe having that information front and center in the README is important to address any potential confusion from users trying to install with the wrong version of Angular — particularly since Angular 15 came out earlier this week, making it the new default version for npm install -g @angular/cli.