Update docs for wiki activity

- Add info to project's index
- Update group activity
- Add info to Wiki doc

doc/user/group/index.md

@@ -248,12 +248,13 @@ These Group Activity Analytics can be enabled with the `group_activity_analytics
 
 A group's **Activity** page displays the most recent actions taken in a group, including:
 
-- **Push events**: Recent pushes to branches
-- **Merge events**: Recent merges
-- **Issue events**: Issues opened or closed
-- **Epic events**: Epics opened or closed
-- **Comments**: Comments opened or closed
-- **Team**: Team members who have joined or left the group
+- **Push events**: Recent pushes to branches.
+- **Merge events**: Recent merges.
+- **Issue events**: Issues opened or closed.
+- **Epic events**: Epics opened or closed.
+- **Comments**: Comments opened or closed.
+- **Team**: Team members who have joined or left the group.
+- **Wiki**: Wikis created, deleted, or updated.
 
 The entire activity feed is also available in Atom format by clicking the
 **RSS** icon.

doc/user/project/index.md

@@ -171,6 +171,13 @@ Read through the documentation on [CI/CD for external repositories](../../ci/ci_
 
 Learn how to [add members to your projects](members/index.md).
 
+## Project activity
+
+To view the activity of a project, navigate to **Project overview > Activity**.
+From there, you can click on the tabs to see **All** the activity, or see it
+filtered by **Push events**, **Merge events**, **Issue events**, **Comments**,
+**Team**, and **Wiki**.
+
 ### Leave a project
 
 **Leave project** will only display on the project's dashboard

doc/user/project/wiki/index.md

@@ -140,6 +140,43 @@ number.
 
 ![Wiki page history](img/wiki_page_history.png)
 
+## Wiki activity records
+
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/14902) in GitLab 12.10.
+> - It's deployed behind a feature flag, disabled by default.
+> - It's enabled on GitLab.com.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-wiki-events-core-only). **(CORE ONLY)**
+
+Wiki events (creation, deletion, and updates) are tracked by GitLab and
+displayed on the [user profile](../../profile/index.md#user-profile),
+[group](../../group/index.md#viewing-group-activity),
+and [project](../index.md#project-activity) activity pages.
+
+### Limitations
+
+Only edits made in the browser or through the API have their activity recorded.
+Edits made and pushed through Git are not currently listed in the activity list.
+  
+### Enable or disable Wiki Events **(CORE ONLY)**
+
+Wiki event activity is under development and not ready for production use. It is
+deployed behind a feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../../administration/troubleshooting/navigating_gitlab_via_rails_console.md#starting-a-rails-console-session)
+can enable it for your instance. You're welcome to test it, but use it at your
+own risk.
+
+To enable it:
+
+```ruby
+Feature.enable(:wiki_events)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:wiki_events)
+```
+
 ## Adding and editing wiki pages locally
 
 Since wikis are based on Git repositories, you can clone them locally and edit