manual: modules are introduced before declared

[bukowa]

Hey!

While reading manual: chapter 24 it states:

Recipes in submodules can be listed with just --list PATH, where PATH is a space- or ::-separated module path:

But modules are introduced in chapter chapter 56 and manual states:

...you’ll need to use the --unstable flag, or set the JUST_UNSTABLE environment variable to use them.

So it's a bit inconsistent and makes me wonder what modules are for 32 chapters! 😃

[casey]

Seems reasonable to me! I added a link to the modules chapter in chapter 24.