Update prerequisites.md (#3050)

* Update prerequisites.md

Document that sudo is required.

* Relocate sudo requirement in prerequisites and reword

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Co-authored-by: Slavi Pantaleev <slavi@devture.com>

docs/prerequisites.md

@@ -18,6 +18,8 @@ If your distro runs within an [LXC container](https://linuxcontainers.org/), you
 
 - [Python](https://www.python.org/) being installed on the server. Most distributions install Python by default, but some don't (e.g. Ubuntu 18.04) and require manual installation (something like `apt-get install python3`). On some distros, Ansible may incorrectly [detect the Python version](https://docs.ansible.com/ansible/latest/reference_appendices/interpreter_discovery.html) (2 vs 3) and you may need to explicitly specify the interpreter path in `inventory/hosts` during installation (e.g. `ansible_python_interpreter=/usr/bin/python3`)
 
+- [sudo](https://www.sudo.ws/) being installed on the server, even when you've configured Ansible to log in as `root`. Some distributions, like a minimal Debian net install, do not include the `sudo` package by default.
+
 - The [Ansible](http://ansible.com/) program being installed on your own computer. It's used to run this playbook and configures your server for you. Take a look at [our guide about Ansible](ansible.md) for more information, as well as [version requirements](ansible.md#supported-ansible-versions) and alternative ways to run Ansible.
 
 - the [passlib](https://passlib.readthedocs.io/en/stable/index.html) Python library installed on the computer you run Ansible. On most distros, you need to install some `python-passlib` or `py3-passlib` package, etc.