mention setmergelist in NEWS

Author: MichaelChirico

NEWS.md

@@ -44,7 +44,7 @@
 
 9. New `cbindlist()` and `setcbindlist()` for concatenating a `list` of data.tables column-wise, evocative of the analogous `do.call(rbind, l)` <-> `rbindlist(l)`, [#2576](https://github.com/Rdatatable/data.table/issues/2576). `setcbindlist()` does so without making any copies. Thanks @MichaelChirico for the FR, @jangorecki for the PR, and @MichaelChirico for extensive reviews and fine-tuning.
 
-10. New `mergelist()` similarly works _a la_ `Reduce()` to recursively merge a `list` of data.tables, [#599](https://github.com/Rdatatable/data.table/issues/599). Different join modes (_left_, _inner_, _full_, _right_, _semi_, _anti_, and _cross_) are supported through the `how` argument; duplicate handling goes through the `mult` argument. Thanks Patrick Nicholson for the FR (in 2013!), @jangorecki for the PR, and @MichaelChirico for extensive reviews and fine-tuning.
+10. New `mergelist()` and `setmergelist()` similarly work _a la_ `Reduce()` to recursively merge a `list` of data.tables, [#599](https://github.com/Rdatatable/data.table/issues/599). Different join modes (_left_, _inner_, _full_, _right_, _semi_, _anti_, and _cross_) are supported through the `how` argument; duplicate handling goes through the `mult` argument. `setmergelist()` carefully avoids copies where one is not needed, e.g. in a 1:1 left join. Thanks Patrick Nicholson for the FR (in 2013!), @jangorecki for the PR, and @MichaelChirico for extensive reviews and fine-tuning.
 
 ### BUG FIXES