Add warnings for Python 3.9. (#1834)

Author: stevepiercy

docs/_inc/_install-python-plone60.md

@@ -11,6 +11,11 @@ Support for Python 3.13.
 Support for Python 3.8.
 ```
 
+```{warning}
+Python 3.9 will reach [end of life in October 2025](https://devguide.python.org/versions/).
+Do not create a new Plone project with Python 3.9.
+```
+
 ```{warning}
 Do not create or activate a Python virtual environment at this time.
 The instructions below will create one.

docs/_inc/_install-python-plone61.md

@@ -1,9 +1,9 @@
 Installing Python is beyond the scope of this documentation.
 However, it is recommended to use a Python version manager, {term}`pyenv`, that allows you to install multiple versions of Python on your development environment without destroying your system's Python.
 
-Plone 6.1 requires Python version {{SUPPORTED_PYTHON_VERSIONS_PLONE61}}.
-
 ```{warning}
 Do not create or activate a Python virtual environment at this time.
 The instructions below will create one.
-```
+```
+
+Plone 6.1 requires Python version {{SUPPORTED_PYTHON_VERSIONS_PLONE61}}.

docs/install/create-project-cookieplone.md

@@ -67,6 +67,14 @@ Plone 6 has both hardware requirements and software prerequisites.
 ```{include} /_inc/_install-python-plone61.md
 ```
 
+Plone 6.0 requires Python version {{SUPPORTED_PYTHON_VERSIONS_PLONE60}}.
+However, Cookieplone does not support Python 3.9.
+
+```{warning}
+Python 3.9 will reach [end of life in October 2025](https://devguide.python.org/versions/).
+Do not create a new Plone project with Python 3.9.
+```
+
 
 #### pipx
 

docs/install/index.md

@@ -47,7 +47,8 @@ Then choose one of the following installation methods.
 If you are following a [Plone training](https://training.plone.org/), it should specify which option to choose.
 
 {doc}`create-project-cookieplone`
-:   This is the recommended way to install Plone for a new project with the Volto frontend.
+:   This is the recommended way to install Plone 6 for a new project with the Volto frontend.
+    Cookieplone requires Python version {{SUPPORTED_PYTHON_VERSIONS_PLONE61}}.
 
 {doc}`/admin-guide/install-buildout`
 :   This is one way to install Plone with the Classic UI frontend.