Document installing the JS machinery

docs/source/development.rst

@@ -3,6 +3,26 @@
 Development
 ===========
 
+Installing Javascript machinery
+-------------------------------
+
+Running the Notebook from the source code on Github requires some Javascript
+tools to build/minify the CSS and Javascript components. We do these steps when
+making releases, so there's no need for these tools when installing released
+versions of the Notebook.
+
+First, install `Node.js <https://nodejs.org/>`_. The installers on the
+Node.js website also include Node's package manager, *npm*. Alternatively,
+install both of these from your package manager. For example, on Ubuntu or Debian::
+
+    sudo apt-get install nodejs-legacy npm
+
+You can then build the Javascript and CSS by running::
+
+    python setup.py css js
+
+This will automatically fetch the remaining dependencies (bower, less) and
+install them in a subdirectory.
 
 CSS live reloading
 ------------------