I've just added you as a contributor, you should now be able to push things. The book should look as a natural continuation of the Arc tutorial. The book should target Anarki, not Arc2. A nice first chapter would be an overview of the most basic Arc macros and functions together with some examples. A chapter on system administration scripts with Arc could also be a good introductory chapter. I would leave web application development as one the last chapters. A chapter on the available third-party libraries could be a good one.
