Sared folders in iCloud

You can't. That's not what iCloud is for. The following is from this Apple document: iCloud: iCloud storage and backup overview

What iCloud backs up

You have important information on your iPhone, iPad, and iPod touch. iCloud automatically backs up your device over Wi-Fi every day while it’s turned on, locked, and connected to a power source. With your device information backed up in iCloud, you can easily set up a new device or restore information on one you already have.

Here’s what iCloud backs up:

• Purchased history for music, movies, TV shows, apps, and booksYour iCloud backup includes information about the content you have purchased, but not the purchased content itself. When you restore from an iCloud backup, your purchased content is automatically downloaded from the iTunes Store, App Store, or iBooks Store. Automatic downloading is based on iTunes in the Cloud availability by country, and previous purchases may be unavailable if they have been refunded or are no longer available in the store.
• Photos and videos in your Camera Roll
• Device settings
• App data
• Home screen and app organization
• iMessage, text (SMS), and MMS messages
• Ringtones
• Visual Voicemail

Consider using Dropbox to share files between computers. The free account will hold up to 2 GB.

OT

If the computers are both Macs, you could try the approach in Winston Churchill's user tip here: https://discussions.apple.com/docs/DOC-2711. Otherwise, use something like Dropbox as Old Toad suggested.