Convert Mediawiki to Markdown (MediaWiki to GFM)

I am using Mediawiki with the "Wikitext" syntax for many years, but now I'm at a point where I want to switch to the "Markdown" syntax.
Here I show you how you can "simply" switch your Mediawiki sites to Markdown files.

First thanks @PhilipAshlock and @OutOfControl for the great GitHub project that makes this even possbile: https://github.com/outofcontrol/mediawiki-to-gfm

Requirements

• PHP: Tested in PHP 7.0, 7.1 and 7.2

sudo apt update
sudo apt -y install php7.3

• Pandoc: Installation instructions are here https://pandoc.org/installing.html (Tested on version 2.0.1.1 and 2.0.2)

sudo apt install pandoc

• Your MediaWiki site: https://www.mediawiki.org/wiki/MediaWiki (Tested on version 1.27.x and 1.29.x)
• Composer: Installation instructions are here https://getcomposer.org/download/

sudo apt install php-xml     
sudo apt install php-mbstring
 
php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php -r "if (hash_file('sha384', 'composer-setup.php') === '906a84df04cea2aa72f40b5f787e49f22d4c2f19492ac310e8cba5b96ac8b64115ac402c8cd292b8a03482574915d1a8') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"