adding documentation on oscar settings and changing BASKET_COOKIE_LIFETIME to OSCAR_BASKET_COOKIE_LIFETIME for consistency

docs/source/index.rst

    web_services
    recipes
    contributing
+   reference
 
 Indices and tables
 ==================

docs/source/reference.rst

+=========
+Reference
+=========
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   reference/settings

docs/source/reference/settings.rst

+=======================
+Oscar specific settings
+=======================
+
+Oscar provides a number of configurable settings used to confugre the system.
+
+.. contents::
+    :local:
+    :depth: 1
+
+Available settings
+==================
+
+OSCAR_DEFAULT_CURRENCY
+----------------------
+
+Default: None (This is a required field)
+
+This should be the symbol of the currency you wish Oscar to use by default.
+
+OSCAR_BASKET_COOKIE_LIFETIME
+----------------------------
+
+Default: 604800 (1 week in seconds)
+
+The time to live for the basket cookie.
+
+Deprecated Settings
+===================
+
+There are currently no deprecated settings in oscar