Clarify instructions for updating PR checks for PRs

Author: mbg

CONTRIBUTING.md

@@ -60,19 +60,20 @@ Here are a few things you can do that will increase the likelihood of your pull
 
     You can start a release by triggering this workflow via [workflow dispatch](https://github.com/github/codeql-action/actions/workflows/update-release-branch.yml).
 1. The workflow run will open a pull request titled "Merge main into releases/v3". Follow the steps on the checklist in the pull request. Once you've checked off all but the last two of these, approve the PR and automerge it.
-1. When the "Merge main into releases/v3" pull request is merged into the `releases/v3` branch, a mergeback pull request to `main` will be automatically created. This mergeback pull request incorporates the changelog updates into `main`, tags the release using the merge commit of the "Merge main into releases/v3" pull request, and bumps the patch version of the CodeQL Action. 
+1. When the "Merge main into releases/v3" pull request is merged into the `releases/v3` branch, a mergeback pull request to `main` will be automatically created. This mergeback pull request incorporates the changelog updates into `main`, tags the release using the merge commit of the "Merge main into releases/v3" pull request, and bumps the patch version of the CodeQL Action.
 1. If a backport to an older major version is required, a pull request targeting that version's branch will also be automatically created.
 1. Approve the mergeback and backport pull request (if applicable) and automerge them.
 
 Once the mergeback and backport pull request have been merged, the release is complete.
 
 ## Keeping the PR checks up to date (admin access required)
 
-Since the `codeql-action` runs most of its testing through individual Actions workflows, there are over two hundred jobs that need to pass in order for a PR to turn green. You can regenerate the checks automatically by running the [update-required-checks.sh](.github/workflows/script/update-required-checks.sh) script:
+Since the `codeql-action` runs most of its testing through individual Actions workflows, there are over two hundred required jobs that need to pass in order for a PR to turn green. It would be too tedious to maintain that list manually. You can regenerate the set of required checks automatically by running the [update-required-checks.sh](.github/workflows/script/update-required-checks.sh) script:
 
-1. By default, this script retrieves the checks from the latest SHA on `main`, so make sure that your `main` branch is up to date.
-2. Run the script. If there's a reason to, you can pass in a different SHA as a CLI argument.
-3. After running, go to the [branch protection rules settings page](https://github.com/github/codeql-action/settings/branches) and validate that the rules for `main`, `v3`, and any other currently supported major versions have been updated.
+- If you run the script without an argument, it will retrieve the set of workflows that ran for the latest commit on `main`. Make sure that your local `main` branch is up to date before running the script.
+- You can specify a commit SHA as argument to retrieve the set of workflows for that commit instead. You will likely want to use this if you have a PR that removes or adds PR checks.
+
+After running, go to the [branch protection rules settings page](https://github.com/github/codeql-action/settings/branches) and validate that the rules for `main`, `v3`, and any other currently supported major versions have been updated.
 
 Note that any updates to checks on `main` need to be backported to all currently supported major version branches, in order to maintain the same set of names for required checks.