Mention the type of addition fields with a rest descriptor

examples/open-records/open_records.md

@@ -4,6 +4,8 @@ A record type that uses either the `{` and `}` delimiters or the `{|` and `|}` d
 
 When the record is open due to using the  `{` and `}` delimiters, the expected type for any additional field is `anydata`. Such records belong to `map<anydata>`. 
 
+When the record is open due to the use of a rest descriptor, the expected type for any additional field is the type specified in the rest descriptor.
+
 Quoted keys can be used to specify fields that are not explicitly specified in an open record type.
 
 ::: code open_records.bal :::