Add implementation details

Author: sjsyrek

README.md

@@ -16,6 +16,8 @@
 
 This library is adapted from [maryamyriameliamurphies.js](https://github.com/sjsyrek/maryamyriameliamurphies.js) with several modifications. It includes functions for creating both eagerly and lazily-evaluated linked list data structures, including infinite lists, and a core subset of functions for working with them. Unlike **maryamyriameliamurphies.js**, however, **lazy-linked-lists** does not implement function currying, partial application, or type checking. It does, however, implement most of the standard [Haskell](https://www.haskell.org) type classes as instance methods, and it also implements the [ES2015 iteration protocols](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols), so you can use them in `for...of` loops.
 
+The lazy lists provided by this library are implemented using the new `Proxy` API in ES2015. Briefly, the lists returned from the most of the list constructors are actually hidden behind proxy objects that trap references to their "tail" property, so that list elements, produced by an ES2015 generator function, are only evaluated on demand. Obviously, if you request the entire tail (by, for example, calling the `length()` function on a list), then the entire tail will be evaluated. You will want to avoid doing that with infinite lists.
+
 Note that as of this writing, most implementations of the ES2015 standard do not yet support [proper tail calls](http://www.2ality.com/2015/06/tail-call-optimization.html). But support is on its way! The newest versions of node and Safari have already rolled it out, and other vendors are surely not far behind. See the top line of this [compatibility chart](https://kangax.github.io/compat-table/es6/) to track the progress of the feature that will make recursively defined, fully-functional, high octane linked lists in JavaScript a reality. Until that fateful day, however, you may be limited to lists of only 10,000 elements or so.
 
 For further details, see the [maryamyriameliamurphies.js documentation](http://sjsyrek.github.io/maryamyriameliamurphies.js/).