Updated README to indicate where to get prebuilt commonmark.js.

README.md

@@ -32,12 +32,13 @@ The parser is very fast, on par with
              --version     Print version
 
 The JavaScript implementation is a single JavaScript file, with
-no dependencies, that can be linked to in an HTML page.  (To build,
-it, do `make js/commonmark.js`---this requires `browserify`, which you
-can get using `npm install -g browserify`.) A command-line
-version (using `node.js`) is also provided (`js/bin/commonmark`), and
-there is a "dingus" for playing with it interactively.  (`make dingus`
-will start this.)
+no dependencies, that can be linked to in an HTML page.  To build,
+it, do `make js/commonmark.js` (this requires `browserify`, which you
+can get using `npm install -g browserify`).  You can also fetch
+a pre-built copy from `http://spec.commonmark.org/js/commonmark.js`.
+A command-line version (using `node.js`) is also provided
+(`js/bin/commonmark`), and there is a "dingus" for playing with it
+interactively.  (`make dingus` will start this.)
 
 [Try it now!](http://jgm.github.io/CommonMark/js/)