update demo code in readme to work with angularjs 1.8

[ajtag]

according to
https://knowledge.exlibrisgroup.com/Primo/Product_Materials/Announcements/Preparing_for_the_Upgrade_to_Angular_1.8_in_Primo%2F%2FPrimo_VE

it looks like the demo code in the README will not be valid after the November2022 update

[rschwab]

Good catch! Yes, specifically the code on this page needs to use the onInit() method.