Perhaps it's just me, but it looks pretty hard to navigate through the code while reading through the book. I have to open and read agents.py to see that it discusses code from Chapters 1 and 2.

There's a notebook called intro.pynb that gives some information about the reasons for this -

A typical module in the repository has the code for a single chapter in the book, but some modules combine several chapters.

But this notebook is not referenced in the README. Besides, it may be nice to have a companion to the book that links, chapter by chapter, section by section, what files or notebooks might be relevant.

Similarly, the instructions to deal with the aima-data submodule are in SUBMODULE.md. But this is not mentioned anywhere in the README. The emptiness of the aima-data subfolder after a git clone might be confusing for newcomers to git. If they move files into the folder from local downloads, it might also complicate the merging of their changes (not 100% sure about this, but it looks like it might be a problem).

I'd like to open a discussion on this before I make any changes, but what do you think, @norvig, @MrDupin?