I'd have expected Peppermint to already have been able to see Windows on the network (?)
To offer shared directories on the network that Windows can see you'll need to install and configure samba .. probably the easiest way to do this would be to install system-config-samba:
sudo apt-get install system-config-samba
(that should also pull in samba as a dependency)
You'll then find a new menu item
menu > System Tools > Samba
where you can set up directories to share.