Update README to use the latest installation commands

[Aiky30]

The commands to install the packages are outdated (https://github.com/Aiky30/djangocms-4-migration#install-the-following-packages):

1. django-cms
2. djangocms-text-ckeditor
3. djangocms-versioning
4. djangocms-alias/

[fsbraun]

I'd suggest (from django-cms-quickstart which I try to keep up-to-date):

# key requirements for django CMS
django-cms>=4.1.0rc3
djangocms-versioning>=2.0.0rc1
djangocms-alias>=2.0.0rc1

# optional, but used in most projects
djangocms-admin-style>=3.2.2

# the default CKEditor - optional, but used in most projects
djangocms-text-ckeditor>=5.1.2