add reference to wl-mirror somewhere in documentation so people can find it

[f0rdprefect]

Description

This is a documentation issue. I tried to figure out how to prepare for presentations, learnt that monitor mirroring does not rerender to the new output, which is ok.

Stumbled across wl-mirror which just works for my use case. Did look into documentation and on github and did not find any pointer that it works.

So wl-mirror is a great choice, IMHO, when trying to present with secondary screen / monitor using hyprland.

[vaxerski]

why not just use the built-in mirroring feature?

Also, moving to wiki...