Let's take this sentence by sentence:

    [Doctests][1] are executable usage examples sometimes found in "docstrings".

This sentence is sound: it succinctly introduces the concept of doctests and provides a link to the relevant section of the Python documentation. Let's leave it as is.

    JavaScript doesn't have docstrings, but inline documentation can be included
    in code comments.

This provides the necessary transition: JavaScript doesn't have docstrings; code comments are the closest (though not very close) approximation.

    doctest tests the accuracy of usage examples in JavaScript and CoffeeScript
    modules.

I agree that this sentence can be improved.

>     Doctest finds usage examples in documenting code comments.

The word "finds" hints that usage examples must be marked up in a particular way in order to be recognized as such. This is useful. Let's take it a step further by saying "finds and evaluates".

Presumably all code comments are documenting. ;)

>     It verifies your documentation and your code by executing those examples.

If we say "finds and evaluates" in the previous sentence, we can drop the second part of this one.

I propose the following:

    [Doctests][1] are executable usage examples sometimes found in "docstrings".
    JavaScript doesn't have docstrings, but inline documentation can be included
    in code comments. doctest finds and evaluates usage examples in code comments
    and reports any inaccuracies. doctest works with JavaScript and CoffeeScript
    modules.