Technically this should probably not be necessary: Duktape module loader
is a fully own implementation based on the CommonJS module loading
specification. The specification is not shipped with the distributable,
just the master repo. But it's perhaps best to mention it in the README
still.
This will make it more probable that the initial compilation works without
investigating a linker error.
Ideally the Makefile would detect readline availability, but that would
require `uname` or some other platform hackery, which is probably too
heavyweight for a simple example Makefile.