Overlayed lacks CLI arguments

[joshqou]

When called from the shell, overlayed provides no command-line arguments and simply creates a window regardless of any supplied arguments.

Overlayed should at minimum provide:

• A simple help argument which describes overlayed's functionality.
• A simple version argument which returns the version & branch of overlayed installed.

Some other additions which would be helpful for power users would be:

• A flag to print information about the current status of discord. i.e: mute & deafened state, voice channel, voice participants, etc.
• Flags to set mute and deafened status, so users could call overlayed to mute/unmute through a global shortcut. (discord keybinds don't work on wayland)
• A monitor-mode to listen to discord RPC events.

Related: #224

Is your feature request related to a problem? Please describe.
Discord doesn't provide any way to easily pull information about the client without tos-prohibited third-party modifications. Overlayed could offer such functionality instead by using its rpc connection.