It's not much different from how you would install it on the real Arduino IDE:
- Download https://github.com/intel/Intel-Pattern-Matching-Technology/archive/master.zip
- (In Arduino Web Editor) Click the Libraries tab.
- Click the upwards arrow icon
- If you get a dialog informing you about importing your entire sketchbook, click "Import"
- Select the downloaded file
- Click "Open"
- Wait until you get a "LIBRARIES SUCCESSFULLY IMPORTED" notification.
- Click "OK"