I recently read Code Reading: The Open Source Perspective by Diomidis Spinellis. I can see how it could be of use to someone trying to contribute to a software project if they didn't have much experience in the language or tools that it used, especially if it was an open source project. I've learned "the hard way" more than I need to know about building and using open source projects, and I've got reasonable experience in a good number of languages and tools, so this book didn't have that much new material for me.

If you'd like to skim a condensed version of the book, you're in luck; flip to the back of the book and check out Appendix E: Maxims for Reading Code, which summarizes the main points of the book in a dozen or so pages. Here's a good one from chapter 1:

You can successfully modify large well-structured systems with only a minimum understanding of their complete functionality. I've always resisted this maxim -- it's more fun to rewrite than modify -- but over the years I've learned that it's true, and modifying existing projects almost always gets the job done faster than starting from scratch, even if the latter seems like more fun.

In fact, all of the maxims from chapter 1 are pretty good, so even if you don't read the whole book, chapter 1 is probably worth it. Chapters 2 through 5 read more like An Introduction to C. The rest of the book seemed pretty intuitive to me -- not many surprises there -- but again, you might find them interesting, so don't avoid the book on my account.

The last chapter is A Complete Example, and shows some of his code reading maxims in practice. If you read that chapter and think you could have done better, maybe this book isn't for you. If you read that chapter and aren't sure you would have thought to do what he did, perhaps the book is worth a closer look.