[docs] Describe the versions of Moodle required for upgrades

Author: andrewnicols

general/development/policies/moodle-versions.md

@@ -0,0 +1,30 @@
+---
+title: Moodle Versions
+tags:
+  - Processes
+  - Core development
+  - Versions
+  - Dependencies
+---
+
+New versions of Moodle are released approximately every six months. Moodle supports upgrading from a previous version. This policy describes how the minimum version to upgrade from is calculated.
+
+## Policy statement
+
+When determining the requirements for a version of Moodle, the following rules apply to supported Moodle Versions to upgrade from:
+
+1. A Long Term Support (LTS) release will always require the _previous_ LTS release (or later) for upgrading.
+2. Other versions of Moodle will the higher of either:
+    - the lowest version of Moodle supported by the minimum PHP version requirement; or
+    - the minimum version required by the previous LTS.
+
+:::tip Examples
+
+- Moodle 4.5 LTS requires Moodle 4.1 LTS or higher because it is an LTS release.
+- Moodle 5.0 has a minimum PHP version of 8.2, therefore it requires Moodle 4.2.3 which was the first version to support PHP 8.2.
+
+:::
+
+## See also
+
+- [PHP Version Policy](./php.md)