Add docs for design filename limits

https://gitlab.com/gitlab-org/gitlab/-/issues/209025

doc/administration/instance_limits.md

@@ -284,6 +284,10 @@ NOTE: **Note:** Set the limit to `0` to disable it.
 
 See the [documentation on Snippets settings](snippets/index.md).
 
+## Design Management limits
+
+See the [Design Management Limitations](../user/project/issues/design_management.md#limitations) section.
+
 ## Push Event Limits
 
 ### Webhooks and Project Services

doc/user/project/issues/design_management.md

@@ -49,6 +49,7 @@ and [PDFs](https://gitlab.com/gitlab-org/gitlab/-/issues/32811) is planned for a
 ## Limitations
 
 - Design uploads are limited to 10 files at a time.
+- From GitLab 13.1, Design filenames are limited to 255 characters.
 - Design Management data
   [isn't deleted when a project is destroyed](https://gitlab.com/gitlab-org/gitlab/-/issues/13429) yet.
 - Design Management data [won't be moved](https://gitlab.com/gitlab-org/gitlab/-/issues/13426)