Update admin area repository settings docs

Update section describing how to select where new repositories will be
stored with description of weighted storages.

doc/administration/gitaly/praefect.md

@@ -656,10 +656,10 @@ Particular attention should be shown to:
    Repository > Repository storage** to make the newly configured Praefect
    cluster the storage location for new Git repositories.
 
-   - The default option is unchecked.
-   - The Praefect option is checked.
+   - The default weight is 0.
+   - The Praefect weight is 100.
 
-   ![Update repository storage](img/praefect_storage_v12_10.png)
+   ![Update repository storage](img/praefect_storage_v13_1.png)
 
 1. Verify everything is still working by creating a new project. Check the
    "Initialize repository with a README" box so that there is content in the

doc/administration/repository_storage_paths.md

@@ -110,7 +110,10 @@ Once you set the multiple storage paths, you can choose where new repositories
 will be stored under **Admin Area > Settings > Repository >
 Repository storage > Storage nodes for new repositories**.
 
-![Choose repository storage path in Admin Area](img/repository_storages_admin_ui_v12_10.png)
+Each storage can be assigned a weight from 0-100. When a new project is created, these weights will be used
+to determine the storage location the repository will be created.
+
+![Choose repository storage path in Admin Area](img/repository_storages_admin_ui_v13_1.png)
 
 Beginning with GitLab 8.13.4, multiple paths can be chosen. New repositories
 will be randomly placed on one of the selected paths.