Document that Cypher 5 became available as a query option in Neo4j 5.21 (neo4j#1307)

Author: JPryce-Aklundh

modules/ROOT/pages/deprecations-additions-removals-compatibility.adoc

@@ -800,6 +800,19 @@ New operators:
 * xref:planning-and-tuning/operators/operators-detail.adoc#query-plan-stateful-shortest-path-into[`StatefulShortestPath(Into)`]
 
 a| Introduced new operators to solve xref:patterns/shortest-paths.adoc[`SHORTEST`] queries.
+
+a|
+label:functionality[]
+label:new[]
+[source, cypher, role="noheader"]
+----
+CYPHER 5
+RETURN 1
+----
+
+a|
+Introduced the ability to prepend queries with `CYPHER 5`.
+This ensures that a query is run using version 5 of Cypher.
 |===
 
 [[cypher-deprecations-additions-removals-5.20]]