Not sure what you're getting at: just make a comment in the thread, i.e. open the post https://www.reddit.com/r/AskHistorians/comments/3boqea/the_technical_side_of_the_wright_brothers and, depending on which interface you are using, either (a: desktop) fill in a comment box and hit 'save', or (b: some mobile apps) click the reply icon, fill in the comment box and hit save.

However, if you are going to cite your own work, be aware of this subreddit's rules regarding sources - which see- in particular that "you are not a source" - see for more - so if your book has not been peer-reviewed, do cite the sources you used in your research.