Provide a couple more examples of acceptable commenting

[dotcode]

After a discussion about reasonable use of comments, we thought it worth providing a couple of extra examples of where comments in code are useful (to complement the general rule that code should be self-documenting).

For example, from @morgaan "comment for tricks dictated by business needs"

[jpw]

I always liked "comments should be why, not what". If documenting what the code is doing, that's probably a code smell.