Added info about Sandstorm Radicale Calendar and Contacts.

Thanks to xet7 !

docs/Platforms/FOSS/Sandstorm/Sandstorm.md

@@ -2,6 +2,14 @@
 
 # Sandstorm at Debian and Ubuntu
 
+### Sandstorm Radicale: Calendars and Contacts
+
+- 2025-08-05
+  - Exporting Calendar and Contacts from Google Calendar and Google Contacts to Sandstorm Radicale works.
+  - Importing Calendar .ics file back to Google Calendar does not work, because .ics file size is 2.1 MB.
+    Google Calendar has problems importing .ics files bigger than 1 MB, it would need manual splitting to multiple files.
+    Sandstorm Radicale can import .ics file 2.1 MB successfully.
+
 ### Sandstorm CloudFlare DNS settings
 
 Sandstorm works when configured to full domain, with CloudFlare SSL/TLS, with Caddy.
@@ -160,4 +168,4 @@ It is not possible to import attachments directly from Trello when using Sandsto
 4. Import board as Wekan board to Sandstorm.
 
 [sandstorm_button]: https://img.shields.io/badge/try-Wekan%20on%20Sandstorm-783189.svg
-[sandstorm_appdemo]: https://demo.sandstorm.io/appdemo/m86q05rdvj14yvn78ghaxynqz7u2svw6rnttptxx49g1785cdv1h
+[sandstorm_appdemo]: https://demo.sandstorm.io/appdemo/m86q05rdvj14yvn78ghaxynqz7u2svw6rnttptxx49g1785cdv1h