README: include links to codespace and colab by pv-pterab-s · Pull Request #3415 · arrayfire/arrayfire

codespace link in a temporary repository. let us move this to arrayfire official codespace repo once we agree on things. colab is same link from www.arrayfire.com homepage

codespace loads in 55 seconds on my end. it can be better if we strip the base docker image to get it to a reasonable size

colab can be 10x faster if the workbook is changed to pull arrayfire from google instead of linode