NEWS updates for minor JSON serialization changes (#1832)

This is a follow-up to #1816 and mongodb/mongo-cxx-driver#1322, documenting minor changes to JSON output subsequent to change f2c1bb7

Author: mdbmes

src/libbson/NEWS

@@ -4,7 +4,10 @@ libbson 1.30.0 (Unreleased)
 Fixes:
 
   * Truncated output of `bson_as_json_with_opts` is changed to no longer split valid UTF-8 sequences.
-
+  * Changes were made to the generated JSON text in some cases:
+      * Previously, empty arrays and documents would serialize with either one or two spaces depending on whether it is nested. Empty arrays and documents now consistently serialize with just one space.
+      * Previously, an array omitted due to the maximum recursion limit would serialize to "{ ... }", as if it were a document. Omitted arrays now serialize to "[ ... ]".
+      * The maximum recursion limit now applies to legacy codewscope documents. Deeply nested scope documents will now be omitted like any other deeply nested document.
 
 
 libbson 1.29.2