The app cms_pico integrate Pico in your Nextcloud. This will allow your users to create and manage their own websites with address like: https://cloud.example.com/sites/my_site/. The source of the website will be stored in the users' files and the Markdown will be formatted by Pico to generate the pages.
Because Pico is using the Markdown format, you should consider enabling the Markdown Editor app.
After the git clone, install the composer dependencies:
composer install
Please check the Wiki for more details.