Better changelog

CHANGELOG.md

@@ -13,9 +13,14 @@ Released: TBD
 - [#420](https://github.com/peggyjs/peggy/pull/420) BREAKING: Node v16+ is now
   required for running the CLI or using Peggy as a library.  Generated code
   still targets older runtimes.
-- [#417](https://github.com/peggyjs/peggy/pull/420) BREAKING: change to
-  AST to allow topLevelInitializer and initializer to be arrays, in support of
-  multi-file inputs.  This will require plugin updates.
+- [#417](https://github.com/peggyjs/peggy/pull/417) BREAKING: change to AST to
+  allow topLevelInitializer and initializer to be arrays, in support of
+  multi-file inputs.  This will require plugin updates.  The CLI and API now
+  take multiple files as input, where the first file is your main library, and
+  subsequent files consist of a library of other rules.  The CLI can take file
+  names of the form `npm:<package-name>/<filename>` to load library rules from
+  an NPM package that is installed relative to the previous non-npm file name,
+  or to the current working directory if this is the first file name.
 
 ### Minor Changes