doc: document .clip support.

Author: Sola-ris

docs/library/index.md

@@ -89,6 +89,7 @@ Preview support for office documents or well-known project file formats varies b
 | Filetype                      | Extensions            | Preview Type                                                               |
 | ----------------------------- | --------------------- | -------------------------------------------------------------------------- |
 | Blender                       | `.blend`, `.blend<#>` | Embedded thumbnail :material-alert-circle:{ title="If available in file" } |
+| Clip Studio Paint             | `.clip`               | Embedded thumbnail                                                         |
 | Keynote (Apple iWork)         | `.key`                | Embedded thumbnail                                                         |
 | Krita[^3]                     | `.kra`, `.krz`        | Embedded thumbnail :material-alert-circle:{ title="If available in file" } |
 | MuseScore                     | `.mscz`               | Embedded thumbnail :material-alert-circle:{ title="If available in file" } |