Expand Group DevOps Adoption documentation

doc/user/group/devops_adoption/index.md

@@ -6,9 +6,11 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Group DevOps Adoption **(ULTIMATE)**
 
-> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/321083) as a [Beta feature](https://about.gitlab.com/handbook/product/gitlab-the-product/#beta) in GitLab 13.11.
-> - [Deployed behind a feature flag](../../../user/feature_flags.md), enabled by default.
-> - Not recommended for production use.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/321083) in GitLab 13.11 as a [Beta feature](https://about.gitlab.com/handbook/product/gitlab-the-product/#beta).
+> - [Deployed behind a feature flag](../../../user/feature_flags.md), disabled by default.
+> - [Enabled by default](https://gitlab.com/gitlab-org/gitlab/-/issues/323159) in GitLab 13.12.
+> - Enabled on GitLab.com.
+> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-group-devops-adoption). **(ULTIMATE SELF)**
 
 This in-development feature might not be available for your use. There can be
 [risks when enabling features still in development](../../feature_flags.md#risks-when-enabling-features-still-in-development).
@@ -41,7 +43,65 @@ With DevOps Adoption you can:
 
 ![DevOps Report](img/group_devops_adoption_v13_11.png)
 
-## Enable or disable Group DevOps Adoption **(ULTIMATE)**
+## Enable data processing
+
+Group DevOps Adoption relies on data that has been gathered by a weekly data processing task.
+This task is disabled by default.
+
+To begin using Group DevOps Adoption, access the feature for the first time. GitLab automatically
+enables the data processing for that group. The group data doesn't appear immediately, because
+GitLab requires around a minute to process it.
+
+## What is displayed
+
+DevOps Adoption displays feature adoption data for the given group
+and any added sub-groups for the current calendar month.
+Each group appears as a separate row in the table.
+For each row, a feature is considered "adopted" if it has been used in a project in the given group
+during the time period (including projects in any sub-groups of the given group).
+
+You should expect adoption to be lower at the beginning of the month,
+before you have had an opportunity to use all the features listed in the table.
+
+In the future [we plan to implement](https://gitlab.com/gitlab-org/gitlab/-/issues/329708)
+a rolling 30-day perspective instead.
+
+## When is a feature considered adopted
+
+A feature is considered "adopted" if it has been used anywhere in the group in the specified time.
+For example, if an issue was created in one project in a group, the group is considered to have
+"adopted" issues in that time.
+
+## No penalties for common adoption patterns
+
+DevOps Adoption is designed not to penalize for any circumstances or practices that are common in DevOps.
+Following this guideline, GitLab doesn't penalize for:
+
+1. Having dormant projects. It's common for groups to have a mix of active and dormant projects,
+   so we should not consider adoption to be low if there are relatively many dormant projects.
+   This means we should not measure adoption by how many projects in the group have used a feature,
+   only by whether a feature was used anywhere in the group.
+1. GitLab adding new features over time. It's common for group feature usage to be consistent
+   over time, so we should not consider adoption to have decreased if GitLab adds features.
+   This means we should not measure adoption by percentages, only total counts.
+
+## Add a sub-group
+
+DevOps Adoption can also display data for sub-groups within the given group,
+to show you differences in adoption across the group.
+To add a sub-group to your Group DevOps Adoption report:
+
+1. Select **Add/remove sub-groups**.
+1. Select the sub-group you want to add and select **Save changes**.
+
+The sub-group data might not appear immediately, because GitLab requires around a minute to collect
+the data.
+
+Please note that the sub-group data might not appear immediately,
+because GitLab requires a few moments to collect the data.
+Generally the data will be visible in less than one minute.
+
+## Enable or disable Group DevOps Adoption **(ULTIMATE SELF)**
 
 Group DevOps Adoption is under development and not ready for production use. It is
 deployed behind a feature flag that is **enabled by default**.