docs(orderBy): clarify how sorting is processed
docs(orderBy): clarify how sorting is processed

An API was passing me numbers as strings (ex. '8.25'), and I was noticing
weird sorting behavior with `orderBy` because it was trying to sort the
numbers alphabetically.

Closes #5436

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js