Adding back useful code comment

Author: Oxyjun

src/content/docs/r2/objects/upload-objects.mdx

@@ -16,6 +16,7 @@ Rclone is a command-line tool which manages files on cloud storage. You can use
 Upload your files to R2 using the `rclone copy` command.
 
 ```sh
+# Upload a single file
 rclone copy /path/to/local/file.txt r2:bucket_name
 
 # Upload everything in a directory