docs: note Python 3.12+ requirement on pip install page

docs/installation/pip.rst

@@ -3,6 +3,11 @@
 Installation with pip
 =====================
 
+.. note::
+   **PyAutoFit** requires **Python 3.12 or later**. If you are on Python
+   3.9, 3.10, or 3.11, ``pip install autofit`` will fail with a "no matching
+   distribution" error. Upgrade Python to 3.12+ before installing.
+
 We strongly recommend that you install **PyAutoFit** in a
 `Python virtual environment <https://www.geeksforgeeks.org/python-virtual-environment/>`_, with the link attached
 describing what a virtual environment is and how to create one.
@@ -32,4 +37,21 @@ Run the ``welcome.py`` script to get started!
 
 .. code-block:: bash
 
-   python3 welcome.py
+   python3 welcome.py
+
+Legacy Python versions
+----------------------
+
+We dropped support for Python 3.9, 3.10, and 3.11 in release ``2026.4.5.3``
+(April 2026). Pre-``2026.4.5.3`` releases on PyPI have been yanked, so they
+will not install via the standard ``pip install autofit`` command.
+
+If you have an existing project that requires a pre-``2026.4.5.3`` version,
+you can still install it explicitly by pinning the version, e.g.:
+
+.. code-block:: bash
+
+    pip install autofit==2025.10.6.1
+
+Yanked releases remain available for explicit pins; only resolver-driven
+fallback is blocked.