Add warning for encryption

src/main.rs

@@ -251,6 +251,10 @@ fn print_preamble_and_warnings(args: &Config) -> Result<(), Box<dyn Error>> {
         ". If not, see <https://www.gnu.org/licenses/>.\n"
     ));
 
+    if args.ephemeral_disk_encryption {
+        error!("Encrypted files are _very_ broken; caveat emptor!");
+    }
+
     if !args.unstable_options.is_empty() {
         warn!("Unstable options are enabled. These options should not be used in production!");
     }