Add repo adoption to FAQ (#22778)

This should be a simple set of steps to achieve
repo adoption.

docs/content/doc/help/faq.en-us.md

@@ -449,3 +449,14 @@ It is highly recommended to back-up your database before running these commands.
 If you are using Cloudflare, turn off the auto-minify option in the dashboard.
 
 `Speed` -> `Optimization` -> Uncheck `HTML` within the `Auto-Minify` settings.
+
+## How to adopt repositories from disk
+
+- Add your (bare) repositories to the correct spot for your configuration (`repository.ROOT`), ensuring they are in the correct layout `<REPO_ROOT>/[user]/[repo].git`.
+  - **Note:** the directory names must be lowercase.
+  - You can also check `<ROOT_URL>/admin/config` for the repository root path.
+- Ensure that the user/org exists that you want to adopt repositories for.
+- As an admin, go to `<ROOT_URL>/admin/repos/unadopted` and search.
+  - Users can also be given similar permissions via config [`ALLOW_ADOPTION_OF_UNADOPTED_REPOSITORIES`]({{< relref "doc/advanced/config-cheat-sheet.en-us.md#repository" >}}).
+- If the above steps are done correctly, you should be able to select repositories to adopt.
+  - If no repositories are found, enable [debug logging]({{< relref "doc/advanced/config-cheat-sheet.en-us.md#repository" >}}) to check for any specific errors.