Clarify neo4j-admin server report --database option (neo4j#1946) (neo4j#1951)

Cherry-picked from neo4j#1946

Author: renetapopova

modules/ROOT/pages/tools/neo4j-admin/neo4j-admin-report.adoc

@@ -18,6 +18,12 @@ You can generate a report covering all databases in the DBMS, a specific databas
 For example, if you run the command `neo4j-admin report --database=ne*`, a report will be generated for all databases that start with "ne".
 If not specified, the tool generates a report for all databases in the DBMS.
 
+[NOTE]
+====
+The `--database` option determines from which database(s) the database-level information is collected.
+It does not influence the DBMS-level information, which is gathered based on the specified classifiers.
+====
+
 .Options
 [options="header", cols="<1m,^1a,<4a"]
 |===