README update to resolve dependency issues on Debian/Ubuntu based distros

[mt206]

Following the How to run examples section I was running into errors like:

fatal error: X11/Xlib.h: No such file or directory
   33 | #include <X11/Xlib.h>

and

fatal error: X11/Xcursor/Xcursor.h: No such file or directory
   37 | #include <X11/Xcursor/Xcursor.h>

I was able to resolve all of these by installing the needed headers by adding the xorg-dev package using:
sudo apt install xorg-dev

Might be useful to add a troubleshooting section to the README or a sidenote to the examples for users who might hit the same problem.

[auroraanna]

I have no idea in what package xorg-dev is in nixpkgs. Seaching for it doesn't yield the right result.