MINOR: [R] Update language in NEWS.md related to GH-41223 (#41368)

### Rationale for this change

This clarifies the language added in #41223, as discussed in a post-merge review in #41223 (comment).

### What changes are included in this PR?

Just a tweak to R's NEWS.md file.

### Are these changes tested?

No.

### Are there any user-facing changes?

No.

Authored-by: Bryce Mecum <[email protected]>
Signed-off-by: Bryce Mecum <[email protected]>

r/NEWS.md

@@ -19,7 +19,7 @@
 
 # arrow 16.0.0.9000
 
-* R functions that users write that use functions that Arrow supports in dataset queries now can be used in queries too. Previously, only functions that used arithmetic operators worked. For example, `time_hours <- function(mins) mins / 60` worked, but `time_hours_rounded <- function(mins) round(mins / 60)` did not; now both work. These are not true user-defined functions (UDFs); for those, see `register_scalar_function()`. (#41223)
+* R functions that users write that use functions that Arrow supports in dataset queries now can be used in queries too. Previously, only functions that used arithmetic operators worked. For example, `time_hours <- function(mins) mins / 60` worked, but `time_hours_rounded <- function(mins) round(mins / 60)` did not; now both work. These are automatic translations rather than true user-defined functions (UDFs); for UDFs, see `register_scalar_function()`. (#41223)
 * `summarize()` supports more complex expressions, and correctly handles cases where column names are reused in expressions. 
 
 # arrow 16.0.0