btrfs: update the Kconfig string for CONFIG_BTRFS_EXPERIMENTAL

The following new features are missing:

- Async checksum

- Shutdown ioctl and auto-degradation

- Larger block size support
  Which is dependent on larger folios.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

fs/btrfs/Kconfig

@@ -115,6 +115,10 @@ config BTRFS_EXPERIMENTAL
 
 	  - extent tree v2 - complex rework of extent tracking
 
-	  - large folio support
+	  - large folio and block size (> page size) support
+
+	  - shutdown ioctl and auto-degradation support
+
+	  - asynchronous checksum generation for data writes
 
 	  If unsure, say N.