add copilot instructions file

[peterj]

Add copilot instructions file to expand the things copilot should look for in the code review: https://docs.github.com/en/copilot/how-tos/copilot-on-github/customize-copilot/add-custom-instructions/add-repository-instructions

[muskiteer]

Hi, I would be like to take this one up if no one is working on this currently.