Missing manpage

[woodsb02]

To be feasible diffutils replacement, a manpage will need to be installed to allow users to learn how to use the various features and arguments.

Similar to diffutils manpage: https://www.man7.org/linux/man-pages/man1/diff.1.html

[pythonbrad]

@woodsb02, For this man page and the help message, I think the current approach of ripgrep can help.
It offers a full control on the message, and it will be easier to respect the current diff man page format.

https://github.com/BurntSushi/ripgrep/tree/cbc598f245f3c157a872b69102653e2e349b6d92/crates/core/flags/doc