10/install md

[rfalkenstein]

I did a re-check of the upgrade process from ILIAS 9 to ILIAS 10.

1. Install a clean ILIAS 9
2. Git checkout release_10 in the same directory
3. ran npm according to docu + composer afterwards (this works and it creates the public/ according to

   ILIAS/composer.json

   Line 21 in fb0d7a5

   "pre-install-cmd": [

   )
4. This means we don't need the step sudo -u www-data mkdir -p public/Customizing/global/plugins anymore
5. However, I added npm and composer below since you should install the locked packages before running an upgrade.