Added example for get file archive

doc/api/repositories.md

@@ -119,7 +119,11 @@ would send an archive in ZIP format.
 Parameters:
 
 - `id` (required) - The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user
-- `sha` (optional) - The commit SHA to download. A tag, branch reference or sha can be used. This defaults to the tip of the default branch if not specified
+- `sha` (optional) - The commit SHA to download. A tag, branch reference, or SHA can be used. This defaults to the tip of the default branch if not specified. For example:
+
+    ```sh
+    curl --header "PRIVATE-TOKEN: <your_access_token>" https://gitlab.com/api/v4/projects/<project_id>/repository/archive?sha=<commit_sha>
+    ```
 
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