Add a disclaimer about include, contain_exactly, and match_array

[mcmire]

When used with an array, these matchers don't assume that the array is in a particular kind of order. Therefore, the diff that SuperDiff produces for them will probably a bit difficult to grok, particularly if you're using fuzzy matcher objects (an_object_having_attributes et al.). In addition, if you have elision enabled, it's actually going to hide details that you need to debug your test properly. Therefore, we should recommend that people use match or even eq as it will lead to a better developer experience.