docs: update contributors guide

CONTRIBUTING.md

@@ -38,7 +38,7 @@ For new code, please ensure:
 
 If you are about to publish the package to `pub.dev`, please make sure that you have done the following:
 
-### Update the changelog.
+### Update the changelog
 
 This is easiest with [cider](https://pub.dev/packages/cider), which follows
 the [Keep a Changelog format](https://keepachangelog.com/en/1.0.0/):
@@ -49,7 +49,20 @@ cider log <type> '<message>'
 
 Where `<type>` is one of `added`, `changed`, `deprecated`, `removed`, `fixed`, `security`, and `<message>` is a short description of the change.
 
-### Update the version
+If you do not wish to use cider, please follow the [Keep a Changelog format](https://keepachangelog.com/en/1.0.0/) and add your changes
+under a new `Unreleased` section.
+
+### Automatic Release
+
+The repo is set to automatically publish to pub.dev when a new version is tagged.
+To trigger an automatic release, run the Release workflow from the Actions tab in GitHub.
+
+The input `Version to bump` is required and should be one of `major`, `minor`, or `patch`,
+according to [Semantic Versioning](https://semver.org/).
+
+### Manual Release
+
+#### Update the version
 
 This is easiest with [cider](https://pub.dev/packages/cider) which follows [Semantic Versioning](https://semver.org/):
 
@@ -65,18 +78,29 @@ As a reminder:
 - minor: backwards-compatible new features
 - major: backwards-incompatible changes
 
-### Finalize the changelog
+If you do not wish to use cider, please update the version in the pubspec file manually.
+
+#### Finalize the changelog
 
 Update the changelog to change from Unreleased to the new version:
 
 ```bash
 cider release
 ```
 
-### Upload the package
+If you do not wish to use cider, please update the changelog manually, by replacing the `Unreleased` title with the new version number and date.
+
+#### Upload the package
 
-Commit your changes for the versio, then upload the package to pub.dev:
+Commit your changes for the version, then upload the package to pub.dev:
 
 ```bash
 dart pub publish
 ```
+
+#### Commit the changelog
+
+After publishing, commit the changelog and pubspec files,
+then create a new release on GitHub.
+
+The release title should be the version number, and the description should be the changelog for the version.