docs: prepare readme for v4 release

Author: mcous

README.md

@@ -9,8 +9,9 @@
 Publish packages to npm automatically in GitHub Actions by updating the version number.
 
 - [Change log][releases]
-- [v2 to v3 migration guide](#v2-to-v3)
-- [v1 to v3 migration guide](#v1-to-v3)
+- [v3 to v4 migration guide](#v3-to-v4)
+- [v2 to v4 migration guide](#v2-to-v4)
+- [v1 to v4 migration guide](#v1-to-v4)
 
 [releases]: https://github.com/JS-DevTools/npm-publish/releases
 
@@ -285,17 +286,29 @@ Examples:
 Major releases of the action and libraries may contain breaking changes, documented here.
 For more detailed change logs, see [releases][].
 
-### v2 to v3
+### v3 to v4
 
-The v3 release does not require any changes to how you use `npm-publish` from `v2`. The version of Node.js used by the action was updated to v20 due to GitHub Action's [deprecation of Node.js v16][node16-deprecation]. The minimum required version of Node.js for the library and CLI remains v16.
+The `v4` release does not require any changes to how you use the `npm-publish` action from `v3`. The action was updated to Node 24 / npm 11.
+
+In the library and CLI, support for Node 16 and Node 18 was dropped in `v4`, and the library API was switched to ESM-only. Library users should switch to ESM or update Node to a version with support for [loading ES modules using `require`][esm-require].
+
+[esm-require]: https://nodejs.org/api/modules.html#loading-ecmascript-modules-using-require
+
+### v2 to v4
+
+The `v4` release does not require any changes to how you use the `npm-publish` action from `v2`. The action was updated to Node 20 in `v3` due to GitHub Action's [deprecation of Node 16][node16-deprecation], and then updated to Node 24 in `v4`.
+
+In the library and CLI, support for Node 16 and Node 18 was dropped in `v4`, and the library API was switched to ESM-only. Library users should switch to ESM or update Node to a version with support for [loading ES modules using `require`][esm-require].
 
 [node16-deprecation]: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/
 
-### v1 to v3
+### v1 to v4
 
 The v2 release made several breaking changes to inputs, outputs, and behaviors that were present in `v1`. The examples below focus on the action, but the same changes are applicable to the library and CLI, too.
 
-#### v2 option changes
+In the library and CLI, support for Node 16 and Node 18 was dropped in `v4`, and the library API was switched to ESM-only. Library users should switch to ESM or update Node to a version with support for [loading ES modules using `require`][esm-require].
+
+#### option changes
 
 The `check-version` and `greater-version-only` boolean options were replaced with the `strategy` option:
 
@@ -335,7 +348,7 @@ The `check-version` and `greater-version-only` boolean options were replaced wit
 
 [publishing-nodejs-packages]: https://docs.github.com/actions/publishing-packages/publishing-nodejs-packages
 
-#### v2 output changes
+#### output changes
 
 The `type` output is now an empty string instead of `'none'` when no release occurs
 
@@ -345,7 +358,7 @@ The `type` output is now an empty string instead of `'none'` when no release occ
 +   if: ${{ steps.publish.outputs.type }}
 ```
 
-#### v2 behavior changes
+#### behavior changes
 
 The `--ignore-scripts` option is now passed to `npm publish` as a security precaution. If you define any publish lifecycle scripts - `prepublishOnly`, `prepack`, `prepare`, `postpack`, `publish`, `postpublish` - we recommend you run that logic as a separate explicit build step.