Add release note about removal of record count

Author: kriszyp

docs/technical-details/release-notes/4.tucker/4.5.0.md

@@ -67,4 +67,7 @@ Glob file handling for specifying files used by components has been improved for
 ### Table.getRecordCount
 `Table.getRecordCount()` is now available to get the number of records in a table.
 
+### Removal of record counts from REST API
+Previously the root path for a resource in the REST API would return a record count. However, this is a significant performance hazard and was never documented to exist, so this has been removed to ensure better performance and reliability.
+
 Note that downgrading from 4.5 to 4.4 is *not* supported.