Update docs on collaborator limits

Author: usha-mandya

docker-hub/billing/index.md

@@ -16,9 +16,13 @@ Docker offers pricing plans that are tailored for individual developers and deve
 
 **For individuals:**
 
-The **Pro** plan includes unlimited public repositories, unlimited private repositories, unlimited collaborators, and 2 parallel builds starting at $5 per month with the annual subscription.
+The **Pro** plan includes unlimited public repositories, unlimited private repositories, unlimited [collaborators](../repos.md#collaborators-and-their-role) for public repositories, one [service account](../repos.md#service-accounts) for private repositories, and 2 parallel builds, starting at $5 per month with the annual subscription.
 
-The **Free** plan includes unlimited public repositories and unlimited collaborators for public repositories at no cost per month.
+> **Note**
+>
+> Pro plans allow one service account for private repositories. For more information, see [service accounts](../repos.md#service-accounts).
+
+The **Free** plan includes unlimited public repositories and unlimited collaborators for public repositories and zero collaborators for private repositories at no cost per month.
 
 **For development teams:**
 

docker-hub/repos.md

@@ -36,7 +36,6 @@ later in the repository settings.
 
 ![Setting page for creating a repo](images/repo-create-details.png)
 
-
 After you hit the **Create** button, you can start using `docker push` to push
 images to this repository.
 
@@ -174,9 +173,24 @@ Status: Downloaded newer image for centos:latest
 
 You now have an image from which you can run containers.
 
-
 ## Starring Repositories
 
 Your repositories can be starred and you can star repositories in return. Stars
 are a way to show that you like a repository. They are also an easy way of
 bookmarking your favorites.
+
+## Service accounts
+
+ A service account is a Docker ID used by a bot for automating the build pipeline for containerized applications. Service accounts are typically used in an automated workflow and do not share Docker IDs with the members in the Team plan.
+
+ To create a new service account:
+
+ 1. Create a new Docker ID.
+ 2. Create a [team](orgs.md#create-a-team) in your organization and grant it read-only access to your private repositories.
+ 3. Add the new Docker ID to your [organization](orgs.md#working-with-organizations).
+ 4. Add the new Docker ID  to the [team](orgs.md#add-a-member-to-a-team) you created earlier.
+ 5. Create a new [personal access token (PAT)](/access-tokens.md) from the user account and use it for CI.
+
+ > **Note**
+ >
+ > If you want a read-only PAT just for your open source repos, or to access official images and other public images, you do not have to grant any access permissions to the new Docker ID.