Warn about rollbacks not working

CHANGELOG.md

@@ -3,8 +3,7 @@ Changelog
 
 For full details see the [releases page](https://mailu.io/1.9/releases.html)
 
-Upgrade should run fine as long as you generate a new compose or stack
-configuration and upgrade your mailu.env.
+Upgrade should run fine as long as you generate a new compose or stack configuration and upgrade your mailu.env. Please note that once you have upgraded to 1.9 you won't be able to roll-back to earlier versions without resetting user passwords.
 
 If you use a reverse proxy in front of Mailu, it is vital to configure the newly introduced env variables REAL_IP_HEADER and REAL_IP_FROM.
 These settings tell Mailu that the HTTP header with the remote client IP address from the reverse proxy can be trusted.

docs/releases.rst

@@ -119,7 +119,7 @@ A short summary of the new features:
 Upgrading
 `````````
 
-Upgrade should run fine as long as you generate a new compose or stack configuration and upgrade your mailu.env.
+Upgrade should run fine as long as you generate a new compose or stack configuration and upgrade your mailu.env. Please note that once you have upgraded to 1.9 you won't be able to roll-back to earlier versions without resetting user passwords.
 
 If you use a reverse proxy in front of Mailu, it is vital to configure the newly introduced environment variables `REAL_IP_HEADER`` and `REAL_IP_FROM`.
 These settings tell Mailu that the HTTP header with the remote client IP address from the reverse proxy can be trusted.