It’s normal to compensate them for their time.
Normally though you don’t modify it after each participant. But for something very niche like following a README (as opposed to an e-commerce flow targeted to the general population) it might be fine, if less rigorous.
As I already mentioned in another comment, I recommend this post for people who want to go a bit deeper: https://www.nngroup.com/articles/usability-testing-101/