This is a super low priority for me. I just want crontab syntax highlighting in my README.md's on GitHub which claims to use this library. If that's true, then thank you. I'm very happy with your work. If not then this is just a common config/code format that you don't support yet.

Language name

crontab

URL of example repository

If you mean an example implementation of the syntax highlighting.
https://github.com/vim/vim/blob/6ffcc58be32aa1b337bc839cfe173b68cfde7085/runtime/syntax/crontab.vim
If you mean examples of crontab files I can provide those as needed. I didn't find any comprehensive examples in a moderately quick search.

URL of syntax highlighting grammar

I'm not aware of a formal highlighting specification. Below are a couple example syntax highlighting implementations.
https://github.com/vim/vim/blob/6ffcc58be32aa1b337bc839cfe173b68cfde7085/runtime/syntax/crontab.vim
https://github.com/textmate/cron.tmbundle/blob/master/Syntaxes/Crontab.tmLanguage < I've never used this one but it's another example

Most popular extensions

I don't know what is meant by this. I suspect that there are no extensions to the crontab format.

Detected language

Crontab files are detected as the crontab filetype by vim/neovim.