Document MongoDB version support policy

Author: timgraham

docs/internals/release-process.rst

@@ -29,6 +29,39 @@ As a concrete example, consider a moment in time between the release of Django
   5.1.x, and any active LTS branches (e.g. 4.2.x, if Django MongoDB Backend
   supported it). They will trigger the release of 5.2.x, 5.1.y, 4.2.z.
 
+MongoDB version support policy
+==============================
+
+Major versions of MongoDB have an end-of-life date and are supported for three
+years beyond that through the `MongoDB Extended Lifecycle Support Add-On
+<https://www.mongodb.com/services/support/enterprise-advanced-support-plans>`_.
+
+The goal of the Django MongoDB Backend MongoDB version support policy is to
+ensure a supported version of Django is available through each MongoDB
+version's extended lifecycle.
+
+The last version of Django to support a given version of MongoDB corresponds to
+the long-term support release of Django whose support extends approximately
+three years after the MongoDB version's end-of-life date.
+
+For example, MongoDB 6.0 reached its end-of-life on July 31, 2025 which means
+its end of extended lifecycle support is July 2028. Since Django 5.2 LTS is
+supported until April 2028 (close enough to July 2028), it's the last version
+of Django to support MongoDB 6.0.
+
+.. csv-table::
+    :header: "Django release series", "Supported MongoDB versions"
+
+    "6.0", "7.0, 8.0"
+    "5.2 LTS", "6.0, 7.0, 8.0"
+
+.. seealso::
+
+    * `Django Supported Versions
+      <https://www.djangoproject.com/download/#supported-versions>`_
+    * `MongoDB Software Lifecycle Schedules
+      <https://www.mongodb.com/legal/support-policy/lifecycles>`_
+
 .. _branch-policy:
 
 Branch policy