Merge pull request #451 from dean-krueger/update-recipe-page

Update recipe page to reflect new oneOrMore requirement

Author: gonuke

.gitignore

@@ -9,6 +9,7 @@ source/user/CYCLUS_INSTALL.rst
 source/user/CYCAMORE_INSTALL.rst
 source/user/DEPENDENCIES.rst
 source/user/CYCAMORE_DEPS.rst
+**/core
 docs.zip
 source/previous/release_table.rst
 

source/user/input_specs/recipe.rst

@@ -1,13 +1,15 @@
-``Recipe`` - Recipe Definition (optional, may appear multiple times)
+``Recipe`` - Recipe Definition (required, may appear multiple times)
 ==========================================================================
 
 The most common resources being exchanged by |Cyclus| agents is a
 :term:`material` which has both a :term:`composition` and a mass.  While the
 composition of a material object may be manipulated over time by the agents
 that transact it, it is often necessary for the user to define a specific
-recipe for a material.  Each ``recipe`` section can be used to define a named
-composition that can then be referenced elsewhere, such as in the data for an
-archetype.
+``recipe`` for a material.  Each ``recipe`` section can be used to define a 
+named composition that can then be referenced elsewhere, such as in the data 
+for an archetype. Though at least one ``recipe`` block is required in every 
+|Cyclus| input file, it should be noted that it is possible to define a dummy 
+``recipe`` and not use it should that be desired. 
 
 A ``recipe`` block has the following sections in the following order: