Forward-port missing v2.15.1 upgrading docs to master branch

doc/16-upgrading-icinga-2.md

@@ -37,6 +37,17 @@ alternatives:
 * `ExternalCommandListener` and `LivestatusListener`: Please use the [Icinga 2 API](https://icinga.com/docs/icinga-2/latest/doc/12-icinga2-api/) instead.
 * Windows check-plugins (`check_*.exe`) and `CheckCommand`s: Please use our [PowerShell plugins](https://github.com/Icinga/icinga-powershell-plugins) instead.
 
+## Upgrading to v2.15.1, v2.14.7, or v2.13.13 <a id="upgrading-to-2-15-1"></a>
+
+These three versions include the same fix to the logrotate configuration in `/etc/logrotate.d/icinga2`. As this file is
+tracked as a configuration file by package managers, it may not be updated automatically if it was modified locally.
+After upgrading, make sure to check if there are any files with an extension like `.dpkg-dist` or `.rpmnew` next to it.
+If so, you need to incorporate the changes into your configuration manually.
+
+To verify that the fix was applied correctly, check the contents of `/etc/logrotate.d/icinga2`: If the file uses the
+command `"$DAEMON" internal signal --sig SIGHUP --pid "$pid"` (instead of `kill -HUP "$pid"`), it was upgraded
+correctly.
+
 ## Upgrading to v2.15 <a id="upgrading-to-2-15"></a>
 
 ### Icinga DB <a id="upgrading-to-2-15-icingadb"></a>