I assume with "close" they meant that documentation should be located right there at the code it is documenting. Think Java doc comments (heredoc) or how in Golang you put comments above a function definition which is then automatically turned into documentation.
If documentation is located in an entirely different file, it's easy to modify code and forget to update the corresponding documentation.
I do Android development at work. My workplace equipped me with a laptop that has 16 GB of RAM. It's not enough to have Android Studio open and run the debugger. ADB segfaults because it runs out of memory. Even when I'm not even doing anything at all, Windows already uses a significant portion of RAM available.