If you want to help
Tell your friends about this book. Tell your family. Tell your neighbors, your enemies, your pets. It’s free and it helps a lot.
You can always give me money. Since I don’t and won’t run ads nor sell private user data, the only other way to support this book is to give me money. Note that this is not my full-time job. The more success and revenue this book generates, the more time I will spend writing paragraphs instead of code.
If you don’t care about me personally, think about your contribution as affecting the whole publishing ecosystem. Self-publishing is very time-consuming and takes skill or money. Successful self-published books prove to other authors that they don’t need a publisher. Giving me money, you would be voting for self-publishing with your wallet.