Ask him to put the text onto GH/GL or something so that we can submit PR's with corrections. I haven't founded any code errors yet, but quite a few proofreading things I could point out to him. Parallelism with some of the section headings was the first thing that jumped out at me. e.g:

  1.3 Why Learn Assembly Language
  1.3.1 Gain a Better Understanding of Architecture Issues
  1.3.1 Understanding the Tool Chain
  1.3.1 Improves Understanding of Functions/Procedures

Should all be in the same tense.