Update doc with new Ubuntu version

docs/ubuntu-installation.md

@@ -4,20 +4,19 @@
 
 Download and boot the [latest Ubuntu release](https://releases.ubuntu.com/21.04/ubuntu-21.04-desktop-amd64.iso).
 
-Follow the steps :
+Follow the steps with these customizations:
 
 ![img1](img/ubuntu-installation/1.png)
 ![img2](img/ubuntu-installation/2.png)
 ![img3](img/ubuntu-installation/3.png)
 
-The partitioning is :
+The partitioning is:
 
 1. 256 MB : EFI partition
 2. 20 GB : system partition
 
 ![img4](img/ubuntu-installation/4.png)
 ![img5](img/ubuntu-installation/5.png)
-![img6](img/ubuntu-installation/6.png)
 
 Remove the installation disk and then reboot.
 
@@ -30,14 +29,17 @@ Don't install updates if Ubuntu asks to. The scripts will.
 This is optional but you can add your public SSH key to access the administrator account later:
 
 ```shell
+unset HISTFILE
 sudo mkdir /root/.ssh
-echo 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICeJ9WuncQJG5X51m3M0goX9fohnz9LqlL/AT3OMYBX1' | sudo tee /root/.ssh/authorized_keys
+wget github.com/xpetit.keys
+cat xpetit.keys | sudo tee /root/.ssh/authorized_keys
 sudo chmod 400 !$
+rm xpetit.keys
 ```
 
 ## OS configuration
 
-Run a terminal and type these commands :
+Run a terminal and type these commands:
 
 ```shell
 unset HISTFILE
@@ -52,13 +54,13 @@ The system is now read-only, every data is written to a temporary partition.
 
 The session is password-less.
 
-To gain a superuser terminal, use SSH :
+To gain a superuser terminal, use SSH:
 
 ```console
 user@remote:~$ ssh -p512 root@IP_ADDRESS
 ```
 
-To gain access with read/write access to the filesystem, use this command :
+To gain access with read/write access to the filesystem, use this command:
 
 ```console
 root@ubuntu:~# overlayroot-chroot