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

Now markdownlint covers ./README.md and md files under ./docs only.
However we have a lot of md files under different directories also.
This enables markdownlint for other md files also.

Due to lack of requirements installation on Azure README, the error
can happen:

 "The ipaddr filter requires python's netaddr be installed on the
  ansible controller"

It is nice to add the installation for Azure users.

The ansible-playbook needs to ssh-login to Azure virtual machines with
ssh keypair, and users need to specify ssh_public_keys for their own
ssh public key. The change of ssh_public_keys is mandatory.
So this updates contrib/azurerm/README.md to explain that.
In addition, the path of all.yml was wrong. That also is updated with
this.

install and login links