Add clarity for admin requirement and curl example

doc/api/groups.md

@@ -498,7 +498,7 @@ Parameters:
 
 ## Transfer project to group
 
-Transfer a project to the Group namespace. Available only for admin
+Transfer a project to the Group namespace. Available only to instance administrators.  Transferring projects may fail when tagged packages exist in the project's repository.
 
 ```
 POST  /groups/:id/projects/:project_id
@@ -508,9 +508,13 @@ Parameters:
 
 | Attribute    | Type           | Required | Description |
 | ------------ | -------------- | -------- | ----------- |
-| `id`         | integer/string | yes      | The ID or [URL-encoded path of the group](README.md#namespaced-path-encoding) owned by the authenticated user |
+| `id`         | integer/string | yes      | The ID or [URL-encoded path of the target group](README.md#namespaced-path-encoding) |
 | `project_id` | integer/string | yes      | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) |
 
+```shell
+curl --request POST --header "PRIVATE-TOKEN: <your_access_token>" https://gitlab.example.com/api/v4/groups/4/projects/56
+```
+
 ## Update group
 
 Updates the project group. Only available to group owners and administrators.