Awesome! For now there are a few things you can do depending on your interest and skill level.
All of these things will require a Github account, so please make one.
Firstly, if you find an error or typo in any of the books, report it in the 'Issues' tab on that repo. If you would like to offer changes: fork, edit and create a Pull Request. If you would like to make suggestions, help in another way, or would like to get more involved, you can join the project mailing list.