This way screen reader users will be notified that the element is the
current one.
I'm not entirely sure whether `aria-current="page"` is more appropriate
than `aria-current="true"`, since it's a general helper which can be
used for any collection of links.
A list of links is a very common pattern in the web, and we use it in
many places. Here we're applying it to one of the most simple ones; the
help page.
Generally speaking, I'm not a big fan of helpers, but there are methods
which IMHO qualify as helpers when:
* They do not deal with application objects but mainly strings and
arrays
* They return text or an HTML tag
* Their logic is simple and splitting it into several methods is not
necessary
Many Rails helpers, like `tag`, follow these principles.
