AI policy for projects

Great examples:

• https://github.com/duckdb/duckdb/blob/main/AI_POLICY.md

• https://github.com/BurntSushi/ripgrep/blob/master/AI_POLICY.md

• https://github.com/astral-sh/.github/blob/c5187e200db51bfe11d56e13053d29bd3793fdd8/AI_POLICY.md

https://github.com/home-assistant/android/blob/main/AI_POLICY.md