Correct Sphinx syntax in shipping docs

Underscore does not seem to have meaning in Sphinx, was rendered as-is.

docs/source/howto/how_to_configure_shipping.rst

@@ -16,12 +16,12 @@ How Oscar handles shipping charges
 Oscar uses a "repository" class to manage shipping charges.  The class is used
 in two ways:
 
-* _It provides a list of shipping methods available to the user._  This is used to
+* **It provides a list of shipping methods available to the user.**  This is used to
   generate the content for the shipping methods page of checkout, where the user
   can choose a shipping method.  The methods available generally depend on the
   user, the basket and the shipping address.
 
-* _It allows a shipping method to be retrieved based on a identifying code._  When
+* **It allows a shipping method to be retrieved based on a identifying code.**  When
   a user selects a shipping method during checkout, it is persisted in the
   session using a code.  This code is used to retrieve the chosen shipping
   method when it is required.