Document wiki default branch behavior

doc/user/project/repository/branches/default.md

@@ -37,7 +37,7 @@ the [Git commands you need](#update-the-default-branch-name-in-your-repository)
 
 To update the default branch name for an individual [project](../../index.md):
 
-1. Sign in to GitLab as a user with [Administrator](../../../permissions.md) permissions.
+1. Sign in to GitLab as a user with the [Administrator](../../../permissions.md) role.
 1. In the left navigation menu, go to **Settings > Repository**.
 1. Expand **Default branch**, and select a new default branch.
 1. (Optional) Select the **Auto-close referenced issues on default branch** check box to close
@@ -168,6 +168,7 @@ current default branch, instead of displaying the "not found" page.
 
 ## Resources
 
+- [Configure a default branch for your wiki](../../wiki/index.md)
 - [Discussion of default branch renaming](https://lore.kernel.org/git/pull.656.v4.git.1593009996.gitgitgadget@gmail.com/)
   on the Git mailing list
 - [March 2021 blog post: The new Git default branch name](https://about.gitlab.com/blog/2021/03/10/new-git-default-branch-name/)

doc/user/project/wiki/index.md

@@ -29,6 +29,21 @@ with sibling pages listed in alphabetical order. To view a list of all pages, se
 
 ![Wiki sidebar](img/wiki_sidebar_v13_5.png)
 
+## Configure a default branch for your wiki
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/221159) in GitLab 14.1.
+
+The default branch for your wiki repository depends on your version of GitLab:
+
+- *GitLab versions 14.1 and later:* Wikis inherit the
+  [default branch name](../repository/branches/default.md) configured for
+  your instance or group. If no custom value is configured, GitLab uses `main`.
+- *GitLab versions 14.0 and earlier:* GitLab uses `master`.
+
+For any version of GitLab, you can
+[rename this default branch](../repository/branches/default.md#update-the-default-branch-name-in-your-repository)
+for previously created wikis.
+
 ## Create the wiki home page
 
 When a wiki is created, it is empty. On your first visit, create the landing page