Usage Rules to enable mix ash_ai.gen.usage_rules

[TwistingTwists]

adding a file like -- https://github.com/ash-project/ash/blob/main/usage-rules.md
Helps AI understand the usage of backpackex much better.

then users can sync their usage rules using mix ash_ai.gen.usage_rules .rules backpex
Willing to make a PR!

[Flo0807]

Hey!

Willing to make a PR!

Sure! I'd love to see such a file in Backpex 🙌