ZSH and oh-my-zsh on Ubuntu

@Rayhan

1/2. install-zsh.md

## Installing ZSH Shell:

ZSH is available in the official package repository of Ubuntu 18.04 LTS. So it’s very easy to install.  First update the package repository cache of your Ubuntu 18.04 LTS operating system with the following command:

```bash
sudo apt-get update

Now install ZSH with the following command:

sudo apt-get install zsh

Now that ZSH shell is installed, you can check whether ZSH is working with the following command:

zsh --version