allergies: It may be helpful to explicitly point out that the score components have a certain pattern

In https://github.com/exercism/problem-specifications/blob/master/exercises/allergies/description.md you see the list of score components. It is possible to notice that the score components are all powers of two, but if it is not made clear, a reader may be wondering whether that is intentional and always true of all future components that might be added (https://github.com/exercism/problem-specifications/issues/1284)

The person who fixes this issue should:

* Decide what kind of explanation should be present in the README, out of various possible options:
* Explicitly state something similar to "these values are powers of two" or "each value is twice the previous"
* State something similar to "these values follow a pattern, and future values, if they were ever added, would follow the same pattern" but not state that they are powers of two
* Your idea here
* Add such an explanation in https://github.com/exercism/problem-specifications/blob/master/exercises/allergies/description.md
* Use a word in https://help.github.com/articles/closing-issues-using-keywords/ to indicate you have closed this issue
* OR discuss here why such an explanation is unnecessary and the description is already good as-is