chore: add docs on first-time contributor approval setting (#398)

content/usage/repo_settings.md

@@ -60,12 +60,15 @@ The three settings are:
 
 - **Always Require Approval**: regardless of user, if the webhook event is a pull request from a fork, the build will need to be approved by a repository admin.
 - **Require Approval For Read-Only**: some teams prefer the fork contribution workflow even if users have write permission to the repo. This setting allows those users to not need approval, but read-only users will.
+- **Require Admin Approval for First Time Contributors**: users that have contributed to the repository before will be able to run pull request builds without admin approval. Note: it may take a few hours for a user to be marked as a prior contributor after they have contributed to the repository.
 - **Never Require Approval**: any user will be able to run pull request builds by opening a PR against the repository.
 
 When a build is awaiting approval, the SCM will be updated with the status `pending` with the description `build needs approval from repo admin to run`. 
 
 Repository admins can approve a build in the UI or by using the [CLI](/docs/reference/cli/build/approve).
 
+PR builds that are marked as `pending approval` will auto cancel any previous PR build from the same source (if one exists). This is to prevent a build up of builds pending approval from the same source.
+
 ### Build Limit
 
 The default and max build limit is determined by the platform administrators. These values determine how many builds can be run concurrently for any given repository. These limits exist to prevent any single repository from occupying a large amount of worker resources.