Paragraph about Custom ROMs support in README

From personal experience and from reading many of the problems that users encounter when using this module, I believe that many are unaware of its uncertain compatibility with custom ROMs. Therefore, it would be interesting to add a paragraph about this support detailing: how to know if your ROM is compatible and how to fix it. I've tried to write this short paragraph. Don't hesitate to let me know if anything is unclear, overdeveloped, or too complicated, or if I can add anything, especially to the search terms (for custom ROMs that don't use PixelPropsUtils, for example).