Add AI policy

Duplicate of accrescent/accrescent#788 which I created in wrong repo.

[lberrymage]

Are you suggesting an AI policy for code contributions to Accrescent, or an AI policy for apps submitted to Accrescent?

The former.

[lberrymage]

Then I agree. This is something we should add to our contributing guidelines.

Personally I like secureblue's AI content policy which is short and to the point

In the interest of accuracy, quality, and license of the project, contributing using AI generated code and content of any kind is forbidden.