I think of the Encyclopaedia Britannica of nonparametric statistics as being:
I'm not sure if I would characterize this as introductory or advanced. Many of the sections are a bit terse, in my opinion, and are written with a good deal of mathematical notation. This will be intimidating / off-putting for people who have some math anxiety. On the other hand, it's not really deriving theorems, it's just using mathematical notation to express the ideas. There are some problems included at the end of each section; you could definitely use the book to learn nonparametric statistics.
For a treatment that is much more introductory:
will be much less intimidating, I think. I have skimmed some portions of it, and it seems to be a gentle introduction for people who don't have a strong statistical background. It is very clear, but does not have anything like the depth or coverage of Hollander & Wolfe.