Support
You do not have to. The book is finished, it is free, and you owe nothing for having read it. But people ask, so here is the honest answer.
Better than money
Three things are worth more, and all of them are free.
Tell someone. A book nobody knows about helps nobody. One person who needed it and found it because you mentioned it is worth more than the price of a coffee.
Send a correction. If something here is wrong, or has changed, or was never right, say so. That is a genuine contribution and it improves the book for everyone who downloads it afterwards.
Tell me your story. The parts of this book that came from real experience are the parts readers remember. If something in here saved you, or if something went wrong in a way the book failed to warn you about, that is the raw material for the next version.
Money
Donations are not open yet. A fundraiser is coming too. Both will be added here in a few months.
When they are live, money will go to hosting, the domain, and the hours spent checking whether twenty things are still true. Not the writing, which is done.
If you are broke
Take the book. Say nothing. That is entirely the point of a free book.
And if you want to give something back without money: help someone who looks lost before they ask, buy from the seller with fewer customers, pick up what someone else left, sit with someone eating alone, teach something you know.