mod_invites: Show help if --help passed instead of hostname
Because I couldn't guess the right way to get the help message without
reading the source twice.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec