Hey, if you want to put the reference of your map for downloading, just open "Attachments and other options", there`s down below from text field in the Post reply. Then find "Attach", and click on "Choose File". The file must be in compressed "Zip" file. That`s necessary. For compressing your file, you must pick out your map (or maps), and click on Right button of mouse. Choose "Send to" and pick " Compressed "Zip" file". And just click "Open".
Hope, i help you.