Add help for YARA Language Server (yr-ls --help)

I compiled and tried `yr-ls` binary (YARA LSP server) on OpenBSD/amd64 => my (simple) tests with Neovim and LSP configuration are OK :) I would like to have a simple integrated help for the `yr-ls` binary (none are currently available in `ls/src/main.rs`): - `-h / --help` to display help - `-V / --version` to display version - some other flags to add in the future...