Fix docs warnings

Two links needed to be corrected.

docs/source/howto/how_to_configure_stock_messaging.rst

@@ -2,7 +2,8 @@
 How to configure stock messaging
 ================================
 
-Stock messaging is controlled by an :ref:`availability policy <availabiliy_policies>`
+Stock messaging is controlled by an
+:ref:`availability policy <availability_policies>`
 which is loaded by the :ref:`strategy class <strategy_class>`.
 
 To set custom availability messaging, use your own strategy class to return the

docs/source/topics/key_questions.rst

@@ -77,7 +77,7 @@ factors, including:
 * The payment method used.
 
 Recipes:
-* :doc:`/howto/how_to_configure_tax`
+* :doc:`/howto/how_to_apply_tax_exemptions`
 
 What availability messages are shown to customers?
 --------------------------------------------------