Update src/metaschema/oscal_catalog_metaschema.xml

Fixed grammar.

Co-authored-by: Chris Compton <[email protected]>

src/metaschema/oscal_catalog_metaschema.xml

@@ -146,7 +146,7 @@
                   </allowed-values>
                   <allowed-values target="part[has-oscal-namespace('http://csrc.nist.gov/ns/oscal')]/@name">
                         <enum value="overview">An introduction to a control or a group of controls.</enum>
-                        <enum value="instruction">An information providing directions for a control or a group of controls.</enum>
+                        <enum value="instruction">Information providing directions for a control or a group of controls.</enum>
                   </allowed-values>
             </constraint>
             <remarks>