Update README.md, Debian 12 stable (#1352)

Now that Debian 12 is stable, IWT's team should check to make sure that
CasaOS is stable and then update the wiki

Signed-off-by: kerta1n <36344851+kerta1n@users.noreply.github.com>
Co-authored-by: Tiger Wang <tigerwang@outlook.com>

README.md

@@ -104,7 +104,7 @@ CasaOS fully supports ZimaBoard, Intel NUC, and Raspberry Pi. Also, more compute
 ### System Compatibility
 
 Official Support
-- Debian 11 (✅ Tested, Recommended)
+- Debian 12 (✅ Tested, Recommended)
 - Ubuntu Server 20.04 (✅ Tested)
 - Raspberry Pi OS (✅ Tested)