Update docs for using venv (#8842)

Due many patterns of Linux distributions, it is difficult to install
ansible dependencies as system-wide stably.
Apart of Kubespray doc[1] recommends to use venv to avoid such issue,
and this applies venv usage to the other parts of the doc.

[1]: https://github.com/kubernetes-sigs/kubespray/blob/master/docs/setting-up-your-first-cluster.md#set-up-kubespray

docs/equinix-metal.md

@@ -50,9 +50,12 @@ Pull over Kubespray and setup any required libraries.
 ```bash
 git clone https://github.com/kubernetes-sigs/kubespray
 cd kubespray
-sudo pip install -r requirements.txt
 ```
 
+## Install Ansible
+
+Install Ansible according to [Ansible installation guide](/docs/ansible.md#installing-ansible)
+
 ## Cluster Definition
 
 In this example, a new cluster called "alpha" will be created.