Specifically I fixed a lot of article usage. I did my best to maintain the flow of the document with only minor rearranging of words. If I was unsure of something I left it as it was, as I did not want to possibly corrupt any important technical details.
Links to other parts had absolute URLs, so they were pointing to the
same page, regardless of where they were located. E.g. pages on gitbooks
links to github.
Make them relative, so they are pointing to the host on which the are
located.