How do I generate an entity-relationship diagram for a SQLite database file?

You should try Vertabelo Database Modeler - it's web-based tool which supports database design for the most popular databases, including SQLite. In Vertabelo you can draw ER Diagrams using its superb graphical interface, and then generate SQL code of your DB model. On the other hand, if you've already got SQL, you can visualize the structure of your database by importing the code into Vertabelo. After successful import, an ER Diagram will be generated. And you can edit it, of course. You can play with Vertabelo without any registration - just for trying it. It's awesome! Click here: https://my.vertabelo.com/try (but remember that you must have Chrome or Safari installed).