Clarify YIELD (#1157)

Co-authored-by: Therese Magnusson <[email protected]>

Author: JPryce-Aklundh

modules/ROOT/pages/clauses/call.adoc

@@ -189,6 +189,8 @@ CALL db.labels() YIELD *
 If the procedure has deprecated return columns, those columns are also returned.
 
 Note that `YIELD *` is only valid in standalone procedure calls.
+Variables must be explicitly named in a `YIELD` clause if other clauses than a single procedure `CALL` are present.
+This restriction simplifies query logic and protects against output variables from the procedure accidentally clashing with other query variables.
 For example, the following is not valid:
 
 .Not allowed
@@ -204,7 +206,7 @@ RETURN count(*) AS results
 ====
 
 `YIELD` can be used to filter for specific results.
-This requires knowing the names of the arguments within a procedure's signature, which can either be found in the link:{neo4j-docs-base-uri}/operations-manual/{page-version}/reference/procedures/[Operations Manual -> Procedures] or returned by a `SHOW PROCEDURES` query.
+This requires knowing the names of the arguments within a procedure's signature, which can either be found in the link:{neo4j-docs-base-uri}/operations-manual/{page-version}/reference/procedures/[Operations Manual -> Procedures] or in the `signature` column returned by a `SHOW PROCEDURES` command (see example below).
 
 .Find the argument names of `db.propertyKeys`
 [source, cypher]