Improve instructions for installing Contao

[zoglo]

Description

The current installation process only ever shows in a note, that the downloaded .phar file may or may not need to be renamed, based on server configuration.

Proposal

I propose to add a numbered list on how to install Contao - Quick Guide

1. Create a folder named public (or web, w/e)
2. Set the Document root on the folder /public
3. Download the contao-manager.phar file from contao.org/download
4. DO NOT rename it to .php locally as (S)FTP does not transfer in BINARY MODE
5. Upload the contao-manager.phar to the /public folder
6. NOW RENAME it to contao-manager.phar.php
7. Call your website example.com/contao-manager.phar.php and set a user account
8. If you want to create an account with a password and NOT A PASSKEY? Click the dropdown (Since Contao Manager 1.10)

Also documenting the following as big crucial information would be good:

Important

The Contao Manager is not associated with the installed Contao Application.

The Backend-User for Contao is DIFFERENT than the user in the Contao Manager

If you install the official contao-demo, the credentials can be found in the front end after installing it or on the official demo website: https://demo.contao.org/#:~:text=If%20you%20like%20to%20see%20the%20administration%20panel%20of%20Contao%2C%20please%20choose%20a%20back%20end%20user%20below%20to%20log%20into%20the%20panel.

Related issues:

• Contao Website: Improve the process of downloading and installing Contao website#157
• Contao Manager: Improve the installation process of the current contao-demo contao-manager#899
• Contao Demo: The k.jones admin account is now disabled, users need to create their own admin account contao-demo#88