Add some documentation on kiosks/public sessions

TBR=bartfab@chromium.org
TBR=poromov@chromium.org
TBR=atwilson@chromium.org

Change-Id: I7517942f5315b8a1d06113d70083c9c587bd1a33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1604280
Commit-Queue: Denis Kuznetsov <antrim@chromium.org>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659003}

docs/enterprise/kiosk_public_session.md

+#Kiosk mode and public sessions (ChromeOS)
+
+When ChromeOS device is enterprise enrolled, organization admins can add two
+special types of users on the device. Those are Public sessions and Kiosk apps.
+
+## Public sessions
+
+Public session can be described as managed guest session: guest mode that is
+controlled by user policy.
+
+It does not have any real google account, it is ephemeral (no data would be
+persisted on the device after session is ended), but organization admins
+still have some control over that: they can pre-install extensions, set
+policies, install certificates.
+
+To set up public session, go to [Admin console](https://admin.google.com) under
+```Device Management > Chrome Management > Device Settings```, ```Kiosk
+settings``` section, and set ```Public session kiosk``` setting to
+```Allow```. You can also configure additional settings.
+
+## Kiosk mode
+
+Kiosk mode is a session that runs a single Chrome/Android app.
+
+It does not have any real google account, it is persistent (data will be
+persisted between kiosk sessions) by default.
+
+Multiple kiosk apps are allowed per device, and they can be launched from system
+shelf on the login screen. Additionally, the administrator can set up one app to
+launch automatically on start-up, in which case login screen is not shown unless
+the user cancels the app launch from the app launch splash screen.
+
+To set up kiosk mode, go to [Admin console](https://admin.google.com) under
+```Device Management > Chrome Management > Device Settings```, ```Kiosk
+settings``` section, add available apps under ```Kiosk apps``` / ```Manage
+Kiosk Applications```.
+
+You can configure kiosk app settings under ```Device Management > Chrome
+Management > Apps & Extensions```