Document release management rules (#9823)

README.md

@@ -26,6 +26,13 @@ It includes a custom framework with an IMAP library derived from [IlohaMail][ilo
 and requires a set of external libraries (see composer.json and jsdeps.json files).
 
 
+RELEASES
+--------
+
+Roundcubemail follows the semantic versioning rules for releases. For more details please read [the RELEASE_MANAGEMENT
+file](RELEASE_MANAGEMENT.md).
+
+
 INSTALLATION
 ------------
 For detailed instructions on how to install Roundcube webmail on your server,

RELEASE_MANAGEMENT.md

@@ -0,0 +1,15 @@
+# Release management
+
+Roundcubemail releases follow the rules of [semantic versioning](https://semver.org). As public API in the sense of that document we consider [the plugin API](https://github.com/roundcube/roundcubemail/wiki/Plugin-API) and the upgrade process.
+
+We fully maintain and support only the latest released version of Roundcubemail.
+
+Only security and similarly critical fixes will be published for the previous minor version, too.
+
+(As an example: Imagine the latest release to be version 1.2.3, and the latest release before 1.2.0 to have been 1.1.5. Then, a security fix would be released in a version 1.2.4, as well as a version 1.1.6. A new feature or uncritical bug fix would only be released in a version 1.2.4.)
+
+For new minor or major version, we might release beta versions in advance, but we don't promise those.
+
+There is no guarantee that a change in the "master" branch will be included in the next release.
+
+Exceptions of these rules may happen, but only for good reasons.