Improve the build instructions and fix the Debian/Ubuntu command

[hardBSDk]

Command fix

The libunwind-dev package gaves the following error on Ubuntu 22.04 :

sudo apt-get install libgtk-3-dev libpthread-stubs0-dev liblz4-dev libx11-dev libx11-xcb-dev libvulkan-dev libsdl2-dev libiberty-dev libunwind-dev libc++-dev libc++abi-dev
[sudo] password for ribbon: 
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
libpthread-stubs0-dev is already the newest version (0.4-1build2).
libpthread-stubs0-dev set to manually installed.
libx11-dev is already the newest version (2:1.7.5-1ubuntu0.3).
libx11-dev set to manually installed.
libsdl2-dev is already the newest version (2.0.20+dfsg-2ubuntu1.22.04.1).
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libunwind-14-dev : Breaks: libunwind-dev
E: Unable to correct problems, you have held broken packages.

This was fixed by removing the libunwind-dev package, comment if you know a better solution if the system is lacking this package.

Documentation improvements

I added necessary duplication of commands to improve the context, improved the formatting and added syntax highlighting on code blocks.