Link to related unorm and prfun packages.

We already mention `unorm` further down in the README, but make a
reference up top in the 'installation' section as well.

README.md

@@ -18,6 +18,10 @@ For node.js:
 
     npm install es6-shim
 
+In both browser and node you may also want to include `unorm`; see the
+[`String.prototype.normalize`](#stringprototypenormalize) section for
+details.
+
 ## Safe shims
 
 * `Map`, `Set` (requires ES5)
@@ -170,6 +174,11 @@ Promise.resolve(5).then(function(value) {
 });
 ```
 
+Note that the ES6 `Promise` specification includes very few methods.
+For a more useful set of utility methods
+(`map`/`reduce`/`bind`/`guard`/etc), you might want to look into the
+[`prfun`](https://github.com/cscott/prfun) package.
+
 Other stuff:
 
 * [ECMAScript 6 drafts](http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts)