The very first lines of 'binutils-2.21/README' file are: " 1 README for GNU development tools 2 3 This directory contains various GNU compilers, assemblers, linkers, 4 debuggers, etc., plus their support routines, definitions, and documentation. 5 6 If you are receiving this as part of a GDB release, see the file gdb/README. 7 If with a binutils release, see binutils/README; if with a libg++ release, 8 see libg++/README, etc. That'll give you info about this 9 package -- supported targets, how to use it, how to report bugs, etc. " - to me it looks senseless and useless. It looks like a very ancient file from the times (if there were such times) when GNU tools were indeed distributed in one tarball/directory. WRT the present day 'binutils' the file is senseless, i.e. it hardly contains any practically useful information.
top level is shared between gcc, binutils, gdb, sim etc.