Update fp-006-textual-definitions.md summary fix

Author: nataled

principles/fp-006-textual-definitions.md

@@ -7,7 +7,7 @@ GO TO: [Recommendations/Requirements](#recommendations-and-requirements) |
 
 ## Summary
 
-The ontology has textual definitions for the majority of its classes and for top level terms in particular.
+The ontology MUST have textual definitions for the majority of its classes and for top level terms in particular.
 
 ## Purpose