Update Readme.md

Readme.md

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-Heroku buildpack: Python
+Unofficial Heroku buildpack: Python + npm dependency resolution
 ========================
 
 This is a [Heroku buildpack](http://devcenter.heroku.com/articles/buildpacks) for Python apps.
 It uses [virtualenv](http://www.virtualenv.org/) and [pip](http://www.pip-installer.org/).
 
+Differences
+-----------
+
+The main difference from the official Python buildpack is support for node dependencies via [npm](http://npmjs.org).
+
+This is accomplished via an `npm_requirements.txt` which must be in the base directory (along with the `requirements.txt` file that is used by pip)
+
+If an `npm_requirements.txt` file is present it works similar to the way you're used to with pip.
+
+Each line of the file is appended to `npm install` so for example
+
+npm_requirements.txt:
+
+    coffee-script
+    less@1.0.0
+
+would result in the following commands being run to resolve the dependencies:
+
+    $ npm install -g coffee-script
+    $ npm install -g less@1.0.0
+
+Why install Node along with Python?
+-----------------------------------
+
+Primarily because it's desirable to use technologies like [less-css](http://lesscss.org/) and [coffeescript](http://coffeescript.org/) on the server (with something like [django compressor](https://github.com/jezdez/django_compressor) for example)
+
 Usage
 -----