Add note about automatic reboot from #6

[ci skip]

README.md

@@ -16,6 +16,11 @@ If you set `unattended_mail` to an e-mail address, make sure `mailx` command is
 
 The role requires unattended-upgrades version 0.70 and newer, which is available since Debian Wheezy and Ubuntu 12.04 respectively. This is due to [Origins Patterns](#origins-patterns) usage; if this is not available on your system, you may use [the first version of the role](https://github.com/jnv/ansible-role-unattended-upgrades/tree/v0.1).
 
+### Automatic Reboot
+
+If you enable automatic reboot feature (`unattended_automatic_reboot`), the role will install `update-notifier-common` package, which is required for detecting and executing reboot after the upgrade.
+**Note:** This feature is not currently supported on Debian Jessie, due to a missing replacement for the said package. Attempt to enable this feature on unsupported system will cause a failure. See [the discussion in #6](https://github.com/jnv/ansible-role-unattended-upgrades/issues/6) for more details.
+
 ## Role Variables
 
 * `unattended_origins_patterns`: array of origins patterns to determine whether the package can be automatically installed, for more details see [Origins Patterns](#origins-patterns) below.