They offer a service that will create a .zim file for a website you specify. Some sites do not package up well, and there is a limit to how much they scrape.The tooling is open source, so you could run the scraper yourself if you needed.

https://www.kiwix.org/en/zim-it-up/

Once you have you zim file for your site, i am not sure of the best way to share them with the community. I seed the official zims i use for as long as is practical and would love to have a community resource of extra content.