Nah, we don't need it yet. Most sites don't need the faq unless they have some large policies/how-tos. We shall probably be able to fit most of our policies in
For example, see the tag on meta.chem. We've got one post of site promo, one post for a homework policy, one for a TeX tutorial, and one guide for closevoting. Currently, all we have is this promo post on Robotics. We could make the closevoting guide. The HW policy post makes no sense to be here, and we probably don't need the TeX guide (we have MathJax enabled, but we may not be using it as much).
On the other hand, RaspberryPi.SE has an empty faq tag.
On the Internet, FAQ has come to mean much more than Frequently Asked Questions. It means "hey, newbie, read this!".
If there are any policies we keep needing to link to, then it may be a good idea to use the faq tag. For now, I'd say we're good :)
Most of the faq pages can be found on the mother meta.