[docs] document support for ansible versions (#8827)

drop note about not supporting ansible 2.9 since we still cover it in
nightly CI

docs/ansible.md

@@ -1,4 +1,35 @@
-# Ansible variables
+# Ansible
+
+## Installing Ansible
+
+Kubespray supports multiple ansible versions and ships different `requirements.txt` files for them.
+Depending on your available python version you may be limited in chooding which ansible version to use.
+
+It is recommended to deploy the ansible version used by kubespray into a python virtual environment.
+
+```ShellSession
+VENVDIR=kubespray-venv
+KUBESPRAYDIR=kubespray
+ANSIBLE_VERSION=2.12
+virtualenv  --python=$(which python3) $VENVDIR
+source $VENVDIR/bin/activate
+cd $KUESPRAYDIR
+pip install -U -r requirements-$ANSIBLE_VERSION.txt
+test -f requirements-$ANSIBLE_VERSION.yml && \
+  ansible-galaxy role install -r requirements-$ANSIBLE_VERSION.yml && \
+  ansible-galaxy collection -r requirements-$ANSIBLE_VERSION.yml
+```
+
+### Ansible Python Compatibility
+
+Based on the table below and the available python version for your ansible host you should choose the appropriate ansible version to use with kubespray.
+
+| Ansible Version | Python Version |
+| --------------- | -------------- |
+| 2.9             | 2.7,3.5-3.8    |
+| 2.10            | 2.7,3.5-3.8    |
+| 2.11            | 2.7,3.5-3.9    |
+| 2.12            | 3.8-3.10       |
 
 ## Inventory
 
@@ -272,9 +303,3 @@ pip uninstall ansible ansible-base ansible-core
 cd kubespray/
 pip install -U .
 ```
-
-**Note:** some changes needed to support ansible 2.10+ are not backwards compatible with 2.9
-Kubespray needs to evolve and keep pace with upstream ansible and will be forced to eventually
-drop 2.9 support. Kubespray CIs use only the ansible version specified in the `requirements.txt`
-and while the `ansible_version.yml` may allow older versions to be used, these are not
-exercised in the CI and compatibility is not guaranteed.