Make sure that every code snippet has a comment that specifies the file path

[phil-opp]

See this comment by sieken on the blog:

[…] I am a complete beginner in Rust, and follow this guide mainly to get a better grasp on operating system "basics". Your tutorials have been very good at explaining the code snippets in a simple manner, but sometimes it gets a bit confusing as to where functions and other code snippets should be placed in the file tree.. If you find the time, could you write the path/filename of where each code snippet goes? I'm sure it would be very helpful to other people who, like me, are not yet intuitive about "what parts go where".

I'm going to add this to the “Second Edition” milestone, but this would be also useful for the first edition, if anyone wants to do it.

[phil-opp]

I think this is done.