add NEWS

Author: ben-schwen

NEWS.md

@@ -16,6 +16,8 @@
 
 1. `nafill()`, `setnafill()` extended to work on logical vectors (part of [#3992](https://github.com/Rdatatable/data.table/issues/3992)). Thanks @jangorecki for the request and @MichaelChirico for the PR.
 
+2. `showProgress` argument and `options("datatable.showProgress")` now accept an integer to control the progress bar update interval in seconds, allowing finer control over progress reporting frequency, [#6514](https://github.com/Rdatatable/data.table/issues/6514). Thanks @ethanbsmith for the report and @ben-schwen for the PR.
+
 ### Notes
 
 1. {data.table} now depends on R 3.5.0 (2018).