Put a proper warning on the ChefSpec page

[tas50]

We need to properly warn users to not use ChefSpec when it's not appropriate. A lot of users believe that they need to hit 100% code coverage for even the most trivial of cookbooks. This easily doubles the work involved in writing a Chef cookbook with near zero return in terms of maintainability. A section that outlined good uses of ChefSpec and bad uses of ChefSpec may be helpful here.

[kagarmoe]

This page no longer exists.

[tas50]

Still a page: https://docs.chef.io/workstation/chefspec/