updated contributing section for changelog generator

Author: sacOO7

CONTRIBUTING.md

@@ -203,7 +203,11 @@ This library uses [semantic versioning](http://semver.org/). For each release, t
 1. Create a branch for the release, named like `release/1.2.4` (where `1.2.4` is what you're releasing, being the new version)
 2. Replace all references of the current version number with the new version number (check the [README.md](./README.md) and [common.gradle](./common.gradle)) and commit the changes
     a. Increment the `versionCode` in the Android project's `build.gradle` by 1
-3. Run the [GitHub Changelog Generator](https://github.com/github-changelog-generator/github-changelog-generator) to update the [CHANGELOG](./CHANGELOG.md): something like: `github_changelog_generator -u ably -p ably-java --since-tag v1.2.3 --output delta.md` and then manually merge the delta contents in to the main change log (where `1.2.3` is the preceding release)
+3. Run [`github_changelog_generator`](https://github.com/github-changelog-generator/github-changelog-generator) to automate the update of the [CHANGELOG](./CHANGELOG.md). This may require some manual intervention, both in terms of how the command is run and how the change log file is modified. Your mileage may vary:
+  - The command you will need to run will look something like this: `github_changelog_generator -u ably -p ably-java --since-tag v1.2.3 --output delta.md --token $GITHUB_TOKEN_WITH_REPO_ACCESS`. Generate token [here](https://github.com/settings/tokens/new?description=GitHub%20Changelog%20Generator%20token).
+  - Using the command above, `--output delta.md` writes changes made after `--since-tag` to a new file.
+  - The contents of that new file (`delta.md`) then need to be manually inserted at the top of the `CHANGELOG.md`, changing the "Unreleased" heading and linking with the current version numbers.
+  - Also ensure that the "Full Changelog" link points to the new version tag instead of the `HEAD`.
 4. Commit [CHANGELOG](./CHANGELOG.md)
 5. Make a PR against `main`
 6. Once the PR is approved, merge it into `main`