Adding 'update' to the glossary

Author: bergerhoffer

contributing_to_docs/term_glossary.adoc

@@ -682,6 +682,14 @@ See link:https://kubernetes.io/docs/concepts/storage/storage-classes/[Storage Cl
 
 == U
 
+''''
+=== update
+
+Usage: update
+
+Use "update" when referring to updating the cluster to a new version. Although "upgrade" is sometimes used interchangeably, "update" is the preferred term to use, for consistency.
+
+
 ''''
 === user-provisioned infrastructure